feat: PDF Viewer translation via context menu and two-mode Action Popupv0.1.0

Add Firefox built-in PDF Viewer support using only public WebExtensions
APIs: a selection context menu ("選択したテキストを翻訳") starts a
translation and the toolbar Action Popup shows the streaming result.
No content-script injection into the privileged PDF Viewer, no PDF.js
internals, no separate windows, no custom viewer (Specifications.md §4.6).

Specification alignment (Phase 1)
- Specifications.md: new requirements PDF-01..04 (PDF selection
  translation), CTX-01..03 (context menu translation), POP-01..06
  (popup two modes); SEL-06 updated to route PDF through the menus API;
  section 13.4 adds a 14-item manual PDF verification checklist; section
  15 removes "Firefox内蔵PDF Viewerへの対応" from out-of-scope
- Design.md: architecture diagram with the menus path, menu-translation
  component, menus permission, popup translation-result state machine
  (idle/starting/streaming/completed/error/cancelled), shared translation
  state (§9.2), context-menu integration phase, test plan and API audit
  checklist items (menus permission scope, no PDF Viewer internals)
- Security.md: menus permission restricted to selection-context
  translation; PDF Viewer treated as privileged browser UI (no injection,
  no wrappedJSObject/cloneInto/exportFunction, no internal DOM access);
  menus.OnClickData.selectionText treated as untrusted input passing the
  same validation pipeline; popup result rendering stays textContent-only

Background (Phase 2)
- translation-service.js (new): the single translation pipeline shared by
  every entry point - selection validation (type/trim/empty/control
  chars/max length), prompt building, Ollama request, session/abort, and
  the shared translation state (requestId, sourceText, translatedText,
  status, model, error, startedAt, source). "source" is metadata only; a
  PDF-specific translation engine does not exist
- menu-translation.js (new): validates menus.OnClickData.selectionText
  and starts a sink-less translation observed via GET_POPUP_STATE
- message-router.js: routes port translations through the shared service;
  new runtime messages GET_POPUP_STATE and REGENERATE_LAST; popup-state
  port handler broadcasts live state (initial push + every chunk/status
  change) so an open popup shows streaming progress in real time
- index.js: registers the selection context menu (contexts: ["selection"]
  only, no menus.onShown) and calls browser.action.openPopup()
  synchronously inside the click user gesture, catching failures so a
  popup-open problem never breaks the translation itself
- manifest.json: permissions now ["storage", "menus"]
- settings-service.js: __resetCacheForTests hook for test isolation

Popup two-mode UI (Phase 3)
- popup.html/js/css: mode nav (設定 / 翻訳). Translation mode shows
  status, model, streaming text (textContent only), user-safe error, and
  copy (Clipboard API only, no execCommand fallback), regenerate (new
  requestId reusing the stored source text) and a settings shortcut.
  Closing the popup never cancels the request; reopening shows the
  latest text and continues receiving chunks live. Initial mode: active
  (starting/streaming) translation wins, otherwise the last tab the user
  picked is restored (storage.local.popupMode, default settings)

Fresh-install model auto-selection
- translation-service.js ensureModelConfigured(): when storage.model is
  empty, pick the first model from the running Ollama and persist it
  before translating, mirroring the popup/options auto-select. A user who
  never opened any settings UI can translate immediately; when Ollama is
  unreachable a clear OLLAMA_UNAVAILABLE message is shown

User-safe error details
- detailForUser(): strips URLs (no internal host names echoed to the UI),
  caps length at 120 chars, drops full JSON response bodies, and hides
  meaningless low-level network errors so the popover/popup shows the
  base message plus at most a short, safe detail

Tests: 85 passed, 0 failed
- selectionText validation (untrusted input pipeline)
- menu selection -> translation -> popup state streaming/completed
- empty selection rejected without starting a request
- streaming status transitions observed through GET_POPUP_STATE
- Ollama unreachable surfaces a user-safe error into popup state
- newer request replaces older state (abort semantics)
- regenerateLast reuses source text with a fresh requestId
- popup-state port receives live broadcasts; wrong port names ignored
- fresh-install auto-select persists the first Ollama model
- error detail sanitization (URL stripping, length cap, JSON drop)
- popup/options smoke tests updated for the two-mode markup
- setupRouter resets the shared settings cache for test isolation

Docs: README documents the two-mode popup and PDF flow; Testing-Results
records automated results and the manual PDF checklist (to be executed).

No git-side surprises: this commit was created explicitly on request
(requirement 18 of the PDF task had deferred commits until now).

1 files changed, 29 insertions, 3 deletions

diff --git a/doc/Security.md b/doc/Security.md
index 956f169..66dbde0 100644
--- a/doc/Security.md
+++ b/doc/Security.md
@@ -196,6 +196,7 @@ Use modern APIs where required:
 | Extension storage | `storage.local` |
 | Long-lived extension communication | `runtime.connect()` / `runtime.Port` |
 | One-shot extension messages | `runtime.sendMessage()` |
+| Selection context menu translation | `menus` (selection context only) |
 | Dynamic script injection, only if needed | `scripting.executeScript()` |
 
 ### 5.4 APIs / Patterns to Avoid
@@ -234,6 +235,7 @@ Expected initial permission set:
 
 ```text
 storage
+menus
 ```
 
 Expected host permission:
@@ -249,6 +251,8 @@ or the minimum equivalent required by the final Ollama-host design.
 
 Page access MAY require content-script match patterns for HTTP/HTTPS pages because translation is initiated by selecting page text.
 
+The `menus` permission is used exclusively for the selection-context translation entry point (context menu "選択したテキストを翻訳"). It MUST NOT be used for any other purpose (no page action items, no tab items, no bookmark items, no launcher items).
+
 Do not add broad privileged permissions for convenience.
 
 Every newly introduced permission MUST be justified in code review.
@@ -260,11 +264,11 @@ Every newly introduced permission MUST be justified in code review.
 The system has three primary trust zones.
 
 ```text
-Untrusted Web Page
+Untrusted Web Page / PDF Viewer selection
        |
-       | selected text
+       | selected text (content script or menus.selectionText)
        v
-Content Script
+Content Script / menu-controller (background)
        |
        | validated extension messages
        v
@@ -324,6 +328,25 @@ The background component owns privileged application operations:
 - request cancellation;
 - Ollama response parsing.
 
+### 7.4 Firefox PDF Viewer and Context Menu Input
+
+Firefox's built-in PDF Viewer is privileged browser UI:
+
+- The extension MUST NOT attempt to inject content scripts into it.
+- The extension MUST NOT access its internal DOM, PDF.js internal objects,
+  `wrappedJSObject`, `cloneInto`, `exportFunction`, or any Firefox-internal
+  URI/API to work around the injection restriction.
+- PDF translation is provided exclusively through the public `menus` API.
+
+`menus.OnClickData.selectionText` is UNTRUSTED input:
+
+- it MUST pass the same validation pipeline as content-script selections
+  (string type check, trim, empty rejection, maximum length, control
+  character handling) before being sent to Ollama;
+- it MUST NOT be treated as trusted control input or rendered as HTML;
+- the translation result MUST be rendered in the Action Popup with
+  `textContent`-style plain-text rendering only.
+
 ---
 
 ## 8. DOM and XSS Rules
@@ -743,6 +766,9 @@ Before declaring implementation complete, verify all of the following.
 - [ ] No deprecated WebExtensions API used when a supported current alternative exists.
 - [ ] Permissions are minimal.
 - [ ] No unnecessary `tabs`, `scripting`, `webRequest`, `cookies`, or `nativeMessaging` permission.
+- [ ] `menus` permission used only for selection-context translation.
+- [ ] No content-script injection or internal DOM access into the Firefox PDF Viewer.
+- [ ] `menus.OnClickData.selectionText` validated before use.
 - [ ] Firefox behavior manually verified in `about:debugging`.
 
 ### DOM / Page Boundary