Add advanced channel diagnostics to the player

[fishcharlie]

Summary

• add an advanced-mode three-dot channel menu with a responsive More Info dialog
• show logical channel, physical source, tuner, provider ID, upstream URL, request header, mapping, and resolution-error details
• resolve diagnostics through the same provider path used by live playback
• protect the no-store diagnostics endpoint with administrator authorization
• document the endpoint in OpenAPI and keep browser smoke fixtures current

Verification

• pnpm run typecheck
• pnpm run lint
• pnpm exec vitest run tests/watch/WatchPage.test.tsx
• node --import tsx --test tests/channel-diagnostics-routes.test.ts
• node --import tsx --test tests/channel-resolver.test.ts
• rendered browser QA at desktop and 390x844 mobile viewports, including focus restoration and console checks

The PostgreSQL Testcontainers suite could not run locally because no container runtime was available; the new route is also covered by a passing production-shaped HTTP test without PostgreSQL.

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