Improve content maturity, reliability and measured performance

[debpalash]

Changes

Improve content browsing, stable playback identities, coherent result snapshots, podcast paging, OPDS search, audio EOF/resume, scanning, shutdown, and web error handling. Reduce Watching polling payloads, bound artwork/decode work, and virtualize native queue/transfer rows.

See docs/maturity-audit.md for scope, evidence, reproduction commands and remaining device/provider validation.

Verification

• Native and headless builds; integrated Zig unit and browse/TV/anime gates pass.
• Feature inventory: 476 passed, zero failures/warnings, 14 skipped using an isolated database.
• JavaScript lifecycle: 46 passed.
• Live audio/catalog: 6 passed; audio advancement passed three consecutive runs.
• Restart: 3 passed without forced shutdown. Static assets: 3 passed. Local library: 2 passed. Action identity: nine rejection checks passed.
• Warm loopback Watching fixture: unchanged response 67 bytes versus 35,298 bytes, 99.81% reduction.

Fresh isolated public-provider checks passed for podcast search (50 rows), radio search (30), comics catalog (20), and NASA RSS (200 episode audio URLs). Native sampling confirms the SDL event loop and idle mpv core, but pixels and graceful native UI shutdown remain unverified. Private-server playback and representative GPU/device performance still need independent validation.

Follow-up fixes provision SQLite for Windows unit tests using the actual MSYS2 native prefix and prevent live fixtures from contacting an existing wildcard listener; real port-collision regressions and setup/auth checks pass.