docs: navidrome deep-link spec (replaces in-app player)

docs/superpowers/specs/2026-09-04-navidrome-link-design.md

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+# Replace In-App Player with Navidrome Deep Link — Design Spec
+
+**Date:** 2026-09-04
+**Status:** Approved design, pending implementation
+**Parent:** docs/superpowers/specs/2026-09-03-wave1-hygiene-listening-design.md (supersedes its "Mini player" section)
+
+## Purpose
+
+The built-in album player (global audio element + mini-bar) is removed. Listening happens in the user's Navidrome web UI; the item page links directly to the matched album there. Rationale: Navidrome's player is better than ours, and the in-app player added a global-audio architecture for a preview-quality experience.
+
+## Removals
+
+- `web/src/player/` (PlayerContext, MiniBar) and their tests; PlayerProvider/MiniBar wiring in `web/src/App.tsx`
+- Backend stream/tracks/played routes (`server/src/routes/streamRoutes.ts`) and their tests
+- api methods `getAlbumTracks`, `markPlayed`, `streamUrl`; types `Track`, `AlbumTracks`; ItemPage's `usePlayer`/`load` wiring and media mocks
+- Media-prototype mocks in `web/test/item.test.tsx` (no audio element remains)
+
+## Changes
+
+- **`GET /api/collection/:id` detail** — `matchedAlbum` gains `webUrl: string`: the Navidrome album URL built server-side as `<subsonic_url>/app/#/album/<subsonicId>` (trailing slashes stripped from the configured base; null-safe — `matchedAlbum` stays null when unmatched, and when no Subsonic config exists `webUrl` is still constructed from the stored URL only if the album row exists; unmatched → null either way).
+- **Item page** — the ▶ Play album button becomes an anchor **"Listen in Navidrome ↗"** (`target="_blank"` `rel="noreferrer"`), shown whenever `matchedAlbum != null` (regardless of rip status — the album exists in Navidrome if it matched).
+- **"Last played X ago"** stays. Stamping now comes solely from library sync reading the server's recently-played list (`getAlbumList2?type=recent`, opportunistic `played`/`playedAt` field). No in-app stamping.
+
+## Unchanged
+
+Stats, loans, rip queue, export/backup, sync, matching, all plan-1/2 APIs except the removed routes.
+
+## Error handling
+
+No new failure modes. The link is a static anchor; a wrong Subsonic URL produces a broken link the same way a wrong URL breaks sync — surfaced by Settings, not the item page.
+
+## Testing
+
+- Backend: detail test asserts `matchedAlbum.webUrl` (`http://n.local/app/#/album/<subsonicId>`); stream tests deleted with the routes
+- Web: item tests assert the link (href + target) replaces the player tests; api.test drops the removed methods; player/minibar test files deleted
+
+## Manual device checklist
+
+- Link opens Navidrome's album page from the phone (PWA → browser tab)