Polish subtitle typography, fix live ASR bilingual display, persist settings

[ycosine]

What changed

Font & subtitle design

• Convert bundled LXGW WenKai Lite from 13 MB TTF to 5 MB WOFF2 (lossless container conversion; THIRD_PARTY_NOTICES.md and OFL references updated). Release zip drops from ~8.7 MB back to ~4 MB.
• Add WenKai (文楷) as a subtitle typography preset and make it the new default; the YouTube overlay now injects the bundled font via @font-face.
• Translated subtitle line renders at 0.9em of the platform caption size (CJK glyphs read larger than Latin at equal px), and the standalone ASR overlay base size is reduced.
• Every overlay line is clamped to max 2 lines (-webkit-line-clamp).

Live ASR bilingual fix

• Bug: the translation line was blanked whenever a partial hypothesis was streaming. In continuous speech a new partial starts right after each commit, so translations effectively never displayed — only the English transcript showed. Translation requests were being made all along; it was a display gate.
• Fix: in bilingual mode the translation line now shows the latest committed cue's translation (lagging one sentence behind the live original), the standard pattern for live translated captions.

Settings persistence

• translation-settings, provider-credentials, and asr-credentials move from chrome.storage.local to chrome.storage.sync — settings survive uninstall/reinstall and follow the signed-in browser profile. Translation cache stays local.
• One-time idempotent local→sync migration runs at background startup (never overwrites existing sync values).
• Chromium manifest gains a fixed key, pinning the extension ID (hioaccickilmocnacnbmfjbcihfgpmdj) so loading an unpacked/zip build from any directory keeps the same identity and storage. Firefox already pins via browser_specific_settings.gecko.id.
• README (EN/ZH) privacy sections updated: keys now live in sync storage and ride the browser's own extension sync when signed in.

Notes for existing installs

• Because the manifest key changes the unpacked extension ID, the first load of this version starts fresh one last time; after reconfiguring once, settings persist across all future reinstalls/updates.
• Users who previously saved settings keep their stored subtitle style; pick 文楷 in Options to adopt the new default look.

Validation

• pnpm type-check, pnpm lint, pnpm -F @extension/content-script test (25 tests), pnpm build, pnpm build:firefox
• Verified dist contains the WOFF2 font, Chromium manifest has key + WOFF2 web-accessible resource, Firefox manifest has no key
• dist size: 15 MB → 5.9 MB

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