Implement getNowPlaying + live Streams on Activity page (#237)

[benders]

Closes #237.

What

• getNowPlaying implemented (was a stub). Fed by scrobble?submission=false now-playing pings, held in a new in-memory NowPlayingService — one entry per (user, client) player, stable playerId, expiring 5 minutes after the last ping. Entries are full Song objects plus username, minutesAgo, playerId, playerName, with starred/playCount annotations.
• Per-user by design (per Nic's comment on the issue): a caller sees only their own active players. The cross-user view is admin-only.
• Activity page: GET /api/admin/hub/activity/active now returns nowPlaying[]; the Streams list shows live playback rows (green pulsing "Playing" badge, user, client, minutes-ago) above the in-flight transfer rows — so a track playing from the SPA, a 3rd-party client, or a Sonos cast is visible for the duration of the listen, not just while bytes move.
• SPA pings: PlayerBar sends scrobble(id, false) on play/resume/track-change and every 2 minutes while playing, on both local and Sonos-cast sinks.
• Bug found by the federation suite: submission was parsed with === "false", but py-sonic sends submission=False (capital F) — the ping was being recorded as a durable play. Now parsed case-insensitively like Java's Boolean.parseBoolean. Added to docs/pitfalls.md.

Not in scope

The broader Activity-page overhaul from the issue comment (restructuring history into local "plays" vs peer "fetches") — this PR adds the live now-playing surface; the history-view rework is a follow-up if wanted.

Testing

• pnpm verify: hub 815, frontend 150 — green
• pnpm lint: zero output
• pnpm test:federation: 84/84 py-sonic compat (incl. upgraded test_get_now_playing exercising the real ping→read flow) + eviction/re-admission acts — green

🤖 Generated with Claude Code

https://claude.ai/code/session_01SwwPcrohddTUN7kmQVedQC

[benders]

FROM @claude:

Working through review feedback on this branch:

1. Vibrdrome missing from Now Playing — confirmed client issue: hub logs show Vibrdrome calls stream/savePlayQueue/createBookmark but never scrobble, so it sends no now-playing pings.
2. Hung transfers — stream.ts pipes with .pipe() + manual events; client abort never fires end/error, entry stuck in Active map forever (confirmed: rows with NULL finished_at in live DB). Fix: pipeline() like federation.ts, + boot-time recovery for orphaned rows. Also splitting Active Streams UI into Now Playing / Transfers.
3. Peer name + format/bitrate for Now Playing — info is available (preferred source lookup); enriching now-playing entries with source/format/bitrate.
4. Duplicate History rows — real duplicate HTTP requests per play, all recording FULL file size because hub slurps upstream even after client abort. Same pipeline fix makes bytes honest; also coalescing consecutive same-track rows in History UI.
5. Track name → album link — adding albumId to stream ops + now-playing entries, linking titles to /albums/:id.

[benders]

FROM @claude:

All five feedback items addressed and deployed to the live hub for testing (not yet committed — awaiting approval):

1. Vibrdrome — client limitation confirmed: hub logs show it never calls scrobble (only stream/savePlayQueue/createBookmark), so it can't appear in Now Playing.
2. Hung transfers — root cause: stream.ts used bare .pipe(); a client abort fired neither end nor error, leaking the active entry forever AND recording full-file byte counts for aborted requests. Now uses stream/promises pipeline() (same as federation.ts). Boot-time recovery closed 155 orphaned rows on the live DB (error='interrupted'). Active section is now split into Now Playing and Transfers.
3. Peer/format/bitrate on Now Playing — yes, available: entries now carry a preferred-source snapshot (source, format, bitrate) resolved at ping time; rendered on the Activity page.
4. Duplicate History rows — clients genuinely issue several HTTP requests per listen; the pipeline fix makes their byte counts honest, and the History list now coalesces consecutive same-listen rows into one ×N row with summed bytes.
5. Track → album link — track titles on Now Playing, Transfers, and History rows link to the album page (album_id added to stream_operations via additive migration; now-playing entries carry it too).

pnpm verify, frontend build, full lint, and pnpm test:federation all green. Docs updated (pitfalls.md, hub-internals.md).