fix: UI translation not applied for PDF viewer

Added cacheScope setting (per-site by default, global available) — per-site mode namespaces IndexedDB keys by hostname so each domain maintains its own independent translation cache
Settings page now lists all cached domains with entry counts, each clearable individually via a "Per-site cache" panel
New CacheModule.getHostnames() and clearByHostname() APIs for granular per-domain cache management

New sendPageContext setting (enabled by default, toggleable in options)
When enabled, the page title and meta description are included in every translation request to LLM providers, improving translation accuracy and context awareness
Only affects LLM providers (OpenAI-compatible / Ollama); non-LLM providers are unaffected
Multilingual Localization System

Added translate-locales.js script for auto-generating UI translations via OpenAI-compatible APIs, with retry logic and placeholder token validation
Expanded UI language support from 2 to 29 languages: Arabic, Czech, Danish, Dutch, Finnish, French, German, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Norwegian, Polish, Portuguese (BR & PT), Romanian, Russian, Spanish, Swedish, Thai, Turkish, Ukrainian, Vietnamese, Chinese (Simplified & Traditional)
Options page UI language selector updated to reflect all 29 languages

Target language and provider selections now use sessionStorage (temporary, per-tab) instead of persisting to browser storage — only the options page persists these settings
Language selector converted to a combobox supporting custom BCP-47 codes
Both settings sync instantly with the content script via SET_TARGET_LANG / SET_PROVIDER messages

Added just i18n command to run the locale translation script
Updated all 28 locale files (14 new keys added)

Added

PDF Translation (Major Feature)

• Built-in PDF viewer with full translation support via PDF.js
• PDF toolbar with Translate/Restore buttons for easy translation control
• Translation state management for PDFs with instant abort on pause
• Bilingual display modes for PDFs (original only, translation only, or side-by-side)
• Smart overlay system for translated text with priority-based visibility
• Original text toggle — click overlays to cycle between translation and original text
• Default provider selection specifically for PDF translations

Bilingual Display

• Three display modes — Off (translations only), Embed (original + translation), Tooltip (hover)
• Per-page toggle in popup to switch between modes on the fly
• PDF-specific handling — display modes are independent from page translations

Mobile Support

• Responsive popup design with optimized spacing for small screens
• Touch-friendly controls with 40px+ tap targets on mobile
• Mobile-optimized CSS for options and viewer pages
• Viewport meta tags for proper mobile rendering

Improved

UI & UX

• Consistent button sizing — all buttons use explicit height (28px desktop, 40px mobile) with flex centering
• Compact popup layout — reduced section padding (6→4px) and margins so all content fits on one screen
• Improved typography — cleaner spacing and visual hierarchy
• Removed redundant UI — eliminated "当前" status below site rules (button active states show current selection)
• PDF viewer layout — flexbox-based layout with optimized scroll behavior

Core Functionality

• Instant pause/resume — network requests abort immediately when paused, automatic rescan on resume
• Provider persistence — remembers selected translation provider per page across refreshes and history navigation
• Event-driven sync — all translation state changes support multi-channel synchronization (popup/auto/rules/manual)
• Instant engine switching — provider dropdown changes take effect immediately
• Language matching fix — case-insensitive target language comparison in site rules

PDF Viewer

• Robust notification bar handling — URL-based checks to prevent bar from appearing on extension pages
• Translation box height — automatically expands to accommodate longer translations
• Visual feedback — inactive translation boxes show dashed borders; clickable at any time
• Simplified rotation — clear visual indicators for cycling between translation/original states

Fixed

• Fixed translated content disappearing when scrolling the page
• Fixed PDF viewer notification bar incorrectly appearing during "ask" mode
• Fixed button height inconsistencies across popup sections
• Fixed popup not fitting all content on one screen
• Fixed language detection not matching target language when case differs (e.g., zh-cn vs zh-CN)

support for deepl and libre translate