feat: Firefox selection translation extension with local Ollama (initial version)

Implement the complete initial version of a Firefox WebExtension (Manifest V3)
that translates selected text on web pages using a local Ollama LLM and shows
the result in a small popover near the selection.

Specification alignment (Phase 0)
- Unified Specifications.md / Design.md / Security.md on the same approach:
  Ollama REST API + Fetch API + NDJSON streaming (no ollama-js SDK dependency)
- Fixed host_permissions to http://localhost/* and http://127.0.0.1/* because
  Firefox match patterns do not support port numbers (bug 1362809/1468162);
  the actual connection target is restricted to localhost/127.0.0.1 + any port
  by application-side validation (defense in depth, OLL-09)
- Clipboard: use navigator.clipboard.writeText() only inside the copy button
  click (user activation); no deprecated execCommand fallback

Implementation (zero dependencies, vanilla JS, no npm/Node required)
- manifest.json: MV3, background.scripts + type:module (event page, no
  service_worker), action popup, options_ui, content_scripts for http/https,
  permissions: storage + localhost host permissions only
- src/shared: constants (ports, limits, presets, error codes), message
  validation, settings schema (defaults / merge / sanitize / buildOptions /
  toApiThinking), system prompt builder (fixed prompt first + user prompt)
- src/background: message-router (runtime.Port streaming + runtime.onMessage
  for model list), translation-session (single active request, abort previous
  on new request, stale chunk suppression), ollama-client (fetch against
  /api/tags and /api/chat with buffering NDJSON line parser tolerant to chunk
  boundaries inside JSON objects, AbortController, host re-validation before
  every request, HTTP status to error-code mapping), settings-service
  (storage.local load/save with validation and fallback to defaults)
- src/content/content.js: single classic script (Firefox does not support ES
  modules in content scripts) with selection detection (selectionchange +
  mouseup + keyup, debounced), Shadow DOM action button, Shadow DOM popover
  with HIDDEN/LOADING/STREAMING/COMPLETED/ERROR state machine, port client
  with requestId-based stale chunk filtering, enabled-state sync via
  storage.onChanged; all dynamic text rendered via textContent only
- src/popup + src/options: full settings UI (enable toggle, Ollama host,
  model list from Ollama with saved-model warning, target language, thinking
  mode, temperature slider 0.0-2.0 step 0.1, context length presets
  4k/8k/16k/32k/128k/256k, seed random/fixed with integer value, user system
  prompt, advanced numeric options with steppers, stop sequences textarea)
- icons generated by tools/make-icons.ps1 (System.Drawing, no external tools)
- build.ps1 packages manifest.json + icons/ + src/ into dist zip, excluding
  tests/, doc/, ollama-js/ and tools/

Tests (71 passed, 0 failed)
- In-browser test runner (tests/test.html) with custom describe/it/assert
  framework; no npm, no Node.js
- Unit: constants sync between content mirror and shared module, Ollama host
  validation (localhost/127.0.0.1 + any port only; rejects external hosts,
  LAN IPs, https, credentials, paths), settings schema defaults and fallback,
  temperature 0.1-step validation, context length presets, seed modes,
  advanced option types, buildOptions omission of unset values and absence of
  tfs_z/mirostat fields, system prompt composition order, message validation
  with selection length boundary values
- Integration: NDJSON streaming across awkward byte boundaries, thinking
  chunk forwarding, malformed line tolerance, error payload mapping, think/
  options inclusion rules, model list, TranslationSession abort semantics,
  settings round-trip with storage.onChanged cache refresh, full port flow
  (started/chunk/completed), newer request aborts older with stale chunk
  discard, malformed message rejection, OLLAMA_UNAVAILABLE and
  INVALID_SETTINGS error paths, untrusted sender rejection

Security audit (Design.md section 24 checklist: all pass)
- No innerHTML/outerHTML/document.write/eval/new Function/localStorage
- No remote JS/CSS/fonts/CDN resources; no inline scripts in extension pages
- Ollama access limited to background; content scripts never fetch Ollama
- Background validates message type/length/requestId; single concurrent
  translation enforced
- Clipboard API only (no execCommand fallback)
- Minimal permissions: storage + localhost host permissions

Docs
- README.md with build/load/usage instructions, API list, permission rationale
- doc/Testing-Results.md with automated test results, security audit results,
  and a 14-item manual Firefox verification checklist (to be executed on a
  real Firefox + Ollama environment)

1 files changed, 71 insertions, 0 deletions

diff --git a/src/shared/constants.js b/src/shared/constants.js
new file mode 100644
index 0000000..76a679c
--- /dev/null
+++ b/src/shared/constants.js
@@ -0,0 +1,71 @@
+/**
+ * Shared constants for the extension.
+ *
+ * NOTE: This module is loaded by ES module contexts (background / popup /
+ * options / tests). The content script is a classic script and duplicates the
+ * small subset it needs (see src/content/content.js). The unit tests assert
+ * that the duplicated constants stay in sync.
+ */
+
+export const PORT_NAME = 'translation-stream';
+
+/** Maximum accepted selection length (characters). */
+export const MAX_SELECTION_LENGTH = 20000;
+
+/** Maximum length of the user-defined system prompt. */
+export const MAX_USER_SYSTEM_PROMPT_LENGTH = 2000;
+
+/** Context length presets (fixed values only). */
+export const CONTEXT_PRESETS = [4096, 8192, 16384, 32768, 131072, 262144];
+
+/** Supported target languages. */
+export const LANGUAGES = [
+  { code: 'ja', label: '日本語' },
+  { code: 'en', label: 'English' },
+  { code: 'zh-CN', label: '简体中文' },
+  { code: 'zh-TW', label: '繁體中文' },
+  { code: 'ko', label: '한국어' },
+  { code: 'fr', label: 'Français' },
+  { code: 'de', label: 'Deutsch' },
+  { code: 'es', label: 'Español' },
+  { code: 'pt', label: 'Português' },
+  { code: 'ru', label: 'Русский' }
+];
+
+/** Thinking mode values accepted by the settings UI. */
+export const THINKING_MODES = ['off', 'on', 'low', 'medium', 'high'];
+
+/** Default Ollama endpoint. */
+export const DEFAULT_OLLAMA_HOST = 'http://localhost:11434';
+
+/** Error codes exchanged between background and content script. */
+export const ERROR_CODES = {
+  INVALID_REQUEST: 'INVALID_REQUEST',
+  TEXT_EMPTY: 'TEXT_EMPTY',
+  TEXT_TOO_LONG: 'TEXT_TOO_LONG',
+  OLLAMA_UNAVAILABLE: 'OLLAMA_UNAVAILABLE',
+  MODEL_NOT_FOUND: 'MODEL_NOT_FOUND',
+  INVALID_SETTINGS: 'INVALID_SETTINGS',
+  REQUEST_ABORTED: 'REQUEST_ABORTED',
+  STREAM_ERROR: 'STREAM_ERROR',
+  UNKNOWN_ERROR: 'UNKNOWN_ERROR'
+};
+
+/** Message types: content -> background (via runtime.Port). */
+export const CONTENT_TO_BG = {
+  TRANSLATE: 'translate',
+  CANCEL: 'cancel'
+};
+
+/** Message types: background -> content (via runtime.Port). */
+export const BG_TO_CONTENT = {
+  STARTED: 'started',
+  CHUNK: 'chunk',
+  COMPLETED: 'completed',
+  ERROR: 'error'
+};
+
+/** Message types: one-shot runtime messages (popup/options -> background). */
+export const RUNTIME_MESSAGES = {
+  LIST_MODELS: 'listModels'
+};
\ No newline at end of file