fix(frontend): issues from the 10-25 Chrome sweep

- Incident detail "← Incidents" used router.back(), so arriving from Live
  or a shared link it went to the map / out of the app. Now a Link.
- Resolved incidents showed "0m elapsed" (manual resolve sets no
  resolved_at, updated_at can predate the last call): end is now the
  latest of resolved_at, updated_at and the newest call.
- Admin: the max-width toggle wrapped the tab bar, so it reflowed on every
  tab switch and left the cursor over e.g. "Close calls". Body only now.
- STT Eval sat on "Loading…" forever when a scanned page had zero matches
  but a next_cursor — the refill effect didn't depend on cursor.
- Trip event blocks used dark-only bg-indigo-950/60: unreadable in light
  mode. Theme tokens now.
- Reassign modal said "connected for the first time" on configured nodes.
- Dark-mode placeholders dimmed + italic; they read as filled-in values.

Frontend unverified locally (no Node, #207); CI build typechecks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/app/globals.css

@@ -219,6 +219,14 @@ html:not(.dark) .border-indigo-800 { border-color: #a5b4fc !important; }
 }
 
 /* ── Form inputs ─────────────────────────────────────────────────────────── */
+/* Placeholders must read as hints, not values: Tailwind's default #9ca3af on
+ * the dark surface looked like filled-in text (e.g. /systems Local Area showed
+ * "Ossining / Westchester" next to "no area set"). Dimmer + italic in dark. */
+.dark input::placeholder,
+.dark textarea::placeholder {
+  color: #5F6B80;
+  font-style: italic;
+}
 html:not(.dark) input:not([type="submit"]):not([type="button"]):not([type="reset"]),
 html:not(.dark) select,
 html:not(.dark) textarea {