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/locales/fr.ts

@@ -1650,6 +1650,27 @@ export const frTranslation = {
     endTooltip: 'Terminer la session',
     leaveTooltip: 'Quitter la session',
     helpTooltip: 'Fonctionnement d\'Orbit',
+    diag: {
+      openTooltip: 'Diagnostic — journal d\'événements copiable',
+      title: 'Diagnostic Orbit',
+      role: 'Rôle',
+      hostTrack: 'ID de piste de l\'hôte',
+      hostPos: 'Position de l\'hôte',
+      guestTrack: 'Mon ID de piste',
+      guestPos: 'Ma position',
+      drift: 'Décalage',
+      stateAge: 'Âge de l\'état',
+      eventLog: 'Journal d\'événements ({{count}})',
+      copyLabel: 'Copier',
+      copyTooltip: 'Copier le journal dans le presse-papiers',
+      clearLabel: 'Effacer',
+      clearTooltip: 'Vider le tampon',
+      empty: 'Aucun événement — ils apparaissent dès qu\'Orbit synchronise.',
+      hint: 'Ouvre ceci avant de reproduire le problème, puis clique Copier et colle dans le rapport.',
+      copied: '{{count}} lignes copiées',
+      copyFailed: 'Impossible de copier dans le presse-papiers',
+      cleared: 'Tampon vidé',
+    },
     helpTitle: 'Fonctionnement d\'Orbit',
     helpIntro: 'Orbit transforme Psysonic en salle d\'écoute partagée. Un hôte choisit la musique ; les invités écoutent en synchro et peuvent suggérer des morceaux.',
     helpHostOnly: '(hôte)',