v0.2.12: Pinned tab session, multi-connection server, SW resilience

What's New

Pinned Tab Session

• bctl tab <id> now pins a tab — all subsequent commands auto-target it
• bctl tab --clear to unpin, bctl tab to show current pin status
• Stale pinned tab auto-clears and retries on failure

Multi-Connection Server

• Server now supports multiple extension WebSocket connections
• Seamless handling of Chrome service worker restarts without dropping commands
• Pending futures only cancelled when all connections are gone

Service Worker Resilience (MV3)

• Reduced waitForTabLoad timeout to 5s to prevent SW termination
• Auto-recover from disconnect on new-tab/navigate commands
• Use lastFocusedWindow instead of unreliable currentWindow in SW context

Screenshot Improvements

• CDP-based screenshot for pinned (non-visible) tabs
• Proper tabId null-check in screenshotViaCDP
• handle_screenshot now respects pinned tab context

Enhanced URL Extraction

• Canvas element support (converts to data URL)
• CSS background-image fallback
• Blob URL async conversion to data URL

Download Improvements

• MIME-based file extension correction for image downloads

Bug Fixes

• Fix stale pin retry to also clean up windowId
• Fix screenshotViaCDP falsy check for tab ID 0
• Move _MIME_EXT to module-level constant