feat(orbit): in-app diagnostics popover with copyable event log (#524)

* feat(orbit): in-app diagnostics popover with copyable event log

Multiple users on Discord report Orbit guests stopping after the first
song with no errors anywhere — Settings → Debug → Export Logs is too
buried for non-technical reporters, and the relevant code branches
have no logging at all (silent fail). This adds a one-click "Copy log"
path right inside the Orbit session bar.

The new Activity-icon button next to Help opens a popover with:

- Live mini-display: role, host vs. guest track id + position, drift,
  age of the host's last state write — all updating once a second.
- Scrolling event log textarea fed by an in-memory ring (200 events).
- Copy + Clear buttons. Copy formats `[ISO] [scope] body` lines and
  drops them on the clipboard — paste straight into a Discord report.

Instrumentation lands at the previously-silent decision points:

- Guest pull tick: full snapshot of host vs. guest state on every read.
- Each branch of the divergence detection in `useOrbitGuest.ts` logs
  which path it took and why (initial / track-change-followed /
  track-change-diverged / play-pause-flip), making the
  "stuck after first song" symptom diagnosable from the buffer alone.
- Host pushes log track id, isPlaying, queue length, guest count.

Events are also bridged to the existing `frontend_debug_log` Tauri
command when Settings → Logging is on Debug, so power users still get
the same data in `psysonic-logs-*.log` for offline triage.

i18n: full `orbit.diag.*` namespace in all eight locales. EN + DE are
native; ES / FR / NB / NL / RU / ZH are first-pass and may want a
polish from native speakers later.

* docs(changelog): add orbit diagnostics popover entry

CHANGELOG.md

@@ -18,6 +18,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Added
 
+### Orbit — in-app diagnostics popover with copyable event log
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), prompted by reports from nzxl + RavingGrob, PR [#524](https://github.com/Psychotoxical/psysonic/pull/524)**
+
+* New **Activity-icon** button in the Orbit session bar opens a diagnostics popover. Live mini-display (role, host vs. guest track, position, drift, state-age) updates once a second; below it, a scrolling **event log textarea** is fed by a 200-entry in-memory ring buffer.
+* **Copy** + **Clear** buttons. Copy drops formatted `[ISO] [scope] body` lines on the clipboard — paste straight into a Discord bug report.
+* Instrumentation lands at every previously-silent decision point in the guest tick (`initial-sync`, `track-change` followed / diverged, `play-pause-flip`) plus host state pushes, so the "stopped after the first song" Orbit symptom is now diagnosable from the buffer alone.
+* Events are also bridged to the existing `frontend_debug_log` command when **Settings → Logging** is on Debug, so power users still get the same data in `psysonic-logs-*.log` for offline triage.
+* i18n: full `orbit.diag.*` namespace across all 8 locales (EN + DE native; ES / FR / NB / NL / RU / ZH first-pass, polish welcome).
+
 ### Player Bar — album context menu on song title right-click
 
 **By [@Psychotoxical](https://github.com/Psychotoxical), PR [#512](https://github.com/Psychotoxical/psysonic/pull/512)**