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

src/hooks/useOrbitHost.ts

@@ -19,6 +19,7 @@ import {
 } from '../api/orbit';
 import { showToast } from '../utils/toast';
 import i18n from '../i18n';
+import { pushOrbitEvent } from '../utils/orbitDiag';
 
 /**
  * Orbit — host-side tick hook.
@@ -137,7 +138,17 @@ export function useOrbitHost(): void {
       try {
         await writeOrbitState(sessionPlaylistId, next);
         lastPushedAtRef.current = Date.now();
-      } catch { /* best-effort; next tick retries */ }
+        pushOrbitEvent('host:push', JSON.stringify({
+          track: next.currentTrack?.trackId ?? null,
+          playing: next.isPlaying,
+          posMs: next.positionMs,
+          queueLen: next.playQueueTotal ?? next.playQueue?.length ?? 0,
+          guests: next.participants.length,
+        }));
+      } catch (e) {
+        pushOrbitEvent('host:push', `WRITE FAILED: ${String(e)}`);
+        /* best-effort; next tick retries */
+      }
     };
 
     /**