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/components/OrbitSessionBar.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useRef, useState } from 'react';
-import { X, RefreshCw, Shuffle, Settings2, Share2, HelpCircle } from 'lucide-react';
+import { X, RefreshCw, Shuffle, Settings2, Share2, HelpCircle, Activity } from 'lucide-react';
 import { useTranslation } from 'react-i18next';
 import { useOrbitStore } from '../store/orbitStore';
 import { useHelpModalStore } from '../store/helpModalStore';
@@ -16,6 +16,7 @@ import OrbitParticipantsPopover from './OrbitParticipantsPopover';
 import OrbitExitModal from './OrbitExitModal';
 import OrbitSettingsPopover from './OrbitSettingsPopover';
 import OrbitSharePopover from './OrbitSharePopover';
+import OrbitDiagnosticsPopover from './OrbitDiagnosticsPopover';
 import ConfirmModal from './ConfirmModal';
 
 /**
@@ -49,10 +50,12 @@ export default function OrbitSessionBar() {
   const [peopleOpen, setPeopleOpen] = useState(false);
   const [settingsOpen, setSettingsOpen] = useState(false);
   const [shareOpen, setShareOpen] = useState(false);
+  const [diagOpen, setDiagOpen] = useState(false);
   const [confirmLeave, setConfirmLeave] = useState(false);
   const peopleBtnRef = useRef<HTMLButtonElement>(null);
   const settingsBtnRef = useRef<HTMLButtonElement>(null);
   const shareBtnRef = useRef<HTMLButtonElement>(null);
+  const diagBtnRef = useRef<HTMLButtonElement>(null);
 
   // Second-level tick just for the shuffle countdown + drift readout —
   // the store itself only ticks at 2.5 s which is too coarse for a smooth
@@ -209,6 +212,18 @@ export default function OrbitSessionBar() {
             <span>{t('orbit.catchUpLabel')}</span>
           </button>
         )}
+        <button
+          ref={diagBtnRef}
+          type="button"
+          className="orbit-bar__settings"
+          onClick={() => setDiagOpen(v => !v)}
+          data-tooltip={t('orbit.diag.openTooltip')}
+          aria-haspopup="dialog"
+          aria-expanded={diagOpen || undefined}
+          aria-label={t('orbit.diag.openTooltip')}
+        >
+          <Activity size={14} />
+        </button>
         <button
           type="button"
           className="orbit-bar__settings"
@@ -247,6 +262,12 @@ export default function OrbitSessionBar() {
           onClose={() => setShareOpen(false)}
         />
       )}
+      {diagOpen && (
+        <OrbitDiagnosticsPopover
+          anchorRef={diagBtnRef}
+          onClose={() => setDiagOpen(false)}
+        />
+      )}
       <OrbitExitModal />
       <ConfirmModal
         open={confirmLeave}