feat: provider model freshness TTL and diagnostic UI (#426)

* feat: add server-side TTL for provider snapshots and model list UI

Provider snapshots cached forever, causing newly available models
(e.g. OpenCode Go minimax, glm) to never appear in the picker.

Server: ProviderSnapshotManager now returns stale data immediately
and kicks off a background re-warm when the snapshot is older than
5 minutes. Injectable TTL/clock for testing.

App: Provider settings rows show model count and are tappable to
open a diagnostic sheet with a read-only model list (label + ID).

* feat: add per-provider refresh for models and diagnostic

* refactor: await refresh completion and clean up diagnostic sheet state

- ProviderSnapshotManager.refresh is now async; session.ts awaits it so
  the RPC ACK reflects real completion instead of just queuing work.
- Preserve models/modes/fetchedAt on entries during targeted refresh so
  the list no longer flashes empty mid-refresh.
- Show "Updated Xs ago" next to the Models count, plus loading and
  error states for the list body.
- Split resetSnapshotToLoading into full vs targeted branches.
- Flatten nested ternary in model list rendering into renderModelsBody.
- Drop redundant local refreshing state and cargo useMemo wrappers.

* fix(app): widen isImeComposingKeyboardEvent type to accept optional fields

TextInputKeyPressEventData has isComposing and keyCode as optional, so
Pick<KeyboardEvent, ...> was too narrow and broke typecheck on main.

packages/app/public/index.html

@@ -51,6 +51,17 @@
       [contenteditable='true'] {
         -webkit-app-region: no-drag !important;
       }
+
+      /* Suppress the browser's default focus outline — it appears on mouse
+         clicks and looks out of place against our themed surfaces. Keep a
+         themed ring for keyboard users via :focus-visible. */
+      *:focus {
+        outline: none;
+      }
+      *:focus-visible {
+        outline: 2px solid #20744A;
+        outline-offset: 2px;
+      }
     </style>
   </head>
   <body>