Fix Strava re-auth when credentials change; add disconnect button

When a user saves new Strava credentials with a different client_id,
auto-delete the existing token (it belongs to a different OAuth app
and will always fail on refresh). Add POST /api/strava/disconnect
endpoint and a "Disconnect from Strava" button in settings, visible
only when connected.

Immediate: deleted diego_p's stale token so he can reconnect.

site/src/pages/settings/index.astro

@@ -124,6 +124,14 @@ import Base from '../../layouts/Base.astro';
           </button>
         </div>
       </form>
+      <div id="strava-disconnect-row" class="hidden mt-4 pt-4 border-t border-zinc-800">
+        <p class="text-xs text-zinc-500 mb-2">Connected to Strava. Disconnect to re-authenticate with different credentials.</p>
+        <button id="strava-disconnect-btn"
+          class="px-4 py-2 rounded-lg text-sm bg-zinc-800 hover:bg-red-900 hover:text-red-300 text-zinc-400 transition-colors">
+          Disconnect from Strava
+        </button>
+        <p id="strava-disconnect-status" class="text-xs mt-2 hidden"></p>
+      </div>
     </section>
 
     <!-- Danger zone -->
@@ -509,10 +517,40 @@ import Base from '../../layouts/Base.astro';
     }
   });
 
+  // ── Strava disconnect ─────────────────────────────────────────────────────────
+
+  async function loadStravaConnection() {
+    try {
+      const r = await fetch('/api/strava/status', { credentials: 'include' });
+      if (!r.ok) return;
+      const d = await r.json();
+      document.getElementById('strava-disconnect-row')!
+        .classList.toggle('hidden', !d.connected);
+    } catch { /* ignore */ }
+  }
+
+  document.getElementById('strava-disconnect-btn')?.addEventListener('click', async () => {
+    const statusEl = document.getElementById('strava-disconnect-status')!;
+    if (!confirm('Disconnect from Strava? You will need to reconnect via OAuth to re-enable sync.')) return;
+    try {
+      const r = await fetch('/api/strava/disconnect', { method: 'POST', credentials: 'include' });
+      if (r.ok) {
+        setStatus(statusEl, 'Disconnected.', true);
+        loadStravaConnection();
+      } else {
+        const d = await r.json();
+        setStatus(statusEl, d.detail ?? 'Failed', false);
+      }
+    } catch {
+      setStatus(statusEl, 'Could not reach server', false);
+    }
+  });
+
   // ── Init ─────────────────────────────────────────────────────────────────────
 
   loadMe();
   loadStorage();
   loadNavPrefs();
   loadStravaCreds();
+  loadStravaConnection();
 </script>