chore(web): extract App.tsx's leaf hooks (#2128)

Phase 1 of #2126. Six hooks move out of `clients/web/src/App.tsx`, taking
its component body from 4,891 to 4,267 lines with no behavior change:

- useThemeToggle       — the light/dark toggle
- useTabUiState        — the nine per-screen `ui` objects, the active tab,
                         the pinned-Protocol ids, and the session reset
- useInspectorStores   — the twelve state managers as one create/destroy
                         lifecycle, their `core/react` hooks, and the
                         pagination-mode selection
- useExportActions     — the eleven Clear / Export / Replay handlers
- useProgressToasts    — `notifications/progress` toasts
- useTaskToasts        — task-status toasts, the cancel confirmation, the
                         taskId -> progress map, and the in-flight
                         tool-call taskId ref

Holding the stores in one slot collapses `setupClientForServer`'s and
`onConfirmRemove`'s dependency arrays from twelve entries to two stable
callbacks; `destroyStores` reads the live set through a ref mirror rather
than the state it also writes.

All six hooks are at 100% on all four coverage dimensions, no `v8 ignore`
needed. Also refreshes the now-stale "~4.5k-line" description of App.tsx
in AGENTS.md and the coverage `include` comment.

Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/hooks/useProgressToasts.ts

@@ -0,0 +1,72 @@
+import { useEffect, useRef } from "react";
+import { notifications } from "@mantine/notifications";
+import type {
+  InspectorClient,
+  InspectorClientEventMap,
+} from "@inspector/core/mcp/index.js";
+import type { TypedEventGeneric } from "@inspector/core/mcp/typedEventTarget.js";
+import {
+  formatProgressToastMessage,
+  PROGRESS_TOAST_AUTOCLOSE_MS,
+  progressToastId,
+} from "../utils/toasts/progressToasts";
+
+/**
+ * Surface incoming `notifications/progress` as toasts so the user can watch a
+ * long-running tool's progress while staying on the tool view — the v2
+ * replacement for v1's always-visible "Server Notifications" shelf (#1414).
+ *
+ * The full notification history still lives in the Protocol tab; these toasts
+ * are the at-a-glance, in-context signal. Toasts are keyed by progress stream
+ * (see `progressToastId`) and replaced per tick, so a chatty server updates one
+ * toast rather than stacking one per tick.
+ */
+export function useProgressToasts(inspectorClient: InspectorClient | null) {
+  // Which progress streams currently have a live toast. Entries are removed
+  // when their toast closes (auto-dismiss or user). A ref (not state) because
+  // it is incidental bookkeeping that must not trigger re-renders.
+  const progressToastIdsRef = useRef<Set<string>>(new Set());
+
+  useEffect(() => {
+    if (!inspectorClient) return;
+    const liveToastIds = progressToastIdsRef.current;
+    const onProgress = (
+      event: TypedEventGeneric<InspectorClientEventMap, "progressNotification">,
+    ) => {
+      const detail = event.detail;
+      const id = progressToastId(detail.progressToken);
+      const message = formatProgressToastMessage(detail);
+      if (liveToastIds.has(id)) {
+        notifications.update({
+          id,
+          title: "Tool progress",
+          message,
+          color: "blue",
+          autoClose: PROGRESS_TOAST_AUTOCLOSE_MS,
+        });
+        return;
+      }
+      liveToastIds.add(id);
+      notifications.show({
+        id,
+        title: "Tool progress",
+        message,
+        color: "blue",
+        autoClose: PROGRESS_TOAST_AUTOCLOSE_MS,
+        onClose: () => liveToastIds.delete(id),
+      });
+    };
+    inspectorClient.addEventListener("progressNotification", onProgress);
+    return () => {
+      inspectorClient.removeEventListener("progressNotification", onProgress);
+      // Dismiss any still-visible progress toasts when the client is swapped
+      // out, then drop the stream bookkeeping. Hiding them (rather than letting
+      // them auto-close up to PROGRESS_TOAST_AUTOCLOSE_MS later) keeps a stale
+      // "Tool progress" toast from lingering into the next session, and avoids
+      // a race where the lingering toast's `onClose` would later delete an id
+      // from the *new* session's set and trigger a duplicate-id re-show.
+      liveToastIds.forEach((id) => notifications.hide(id));
+      liveToastIds.clear();
+    };
+  }, [inspectorClient]);
+}