perf: rest animations, cheaper chat typing and server polls, async per-tool hooks

UI
- No animation runs forever: Sagi moods, the custom pet sprite, status dots
  (pulse-dot, pulse-slow, ping) and the chat shimmer play a few cycles and
  rest. An infinite animation kept the browser drawing 60 frames a second.
- useSagiBrain: frames that only move lastActivityAt by <1 s keep the old
  state; the 1 s tick re-renders only when the mood changes.
- ConversationView and MessageList are memoized and PaneChat passes stable
  callbacks: typing in the chat box no longer re-renders the conversation.
- The chat's 700 ms menu poll reads plain text first and scans the terminal
  cell by cell (reusing one cell) only when a row could be a menu cursor row.

Server
- GET /sessions/:id/transcript?after=N skips lines <= N before JSON.parse.
- GET /sessions/:id/outline is cached until the session's events change.
- broadcastLane uses the cached tmux.liveSessions(); tmux.hasSession answers
  "yes" from the fresh shared list instead of a synchronous spawn (50-150 ms
  per psmux call on Windows, blocking terminal echo).
- pane-mode polls every 150 ms; writeHourly writes only changed hour buckets.
- /api/metrics: agenthub_event_loop_delay_seconds{quantile}.

Hooks
- PreToolUse/PostToolUse run with "async": true (settings installer,
  plugin.json, S3 managed settings): Claude Code no longer waits a Node start
  before and after every tool call.

Committed with --no-verify at the owner's request: the pre-commit full server
suite fails on 9 tests that fail identically on 0c2f498 (lane-sync merge: no
git identity on this host; read-pool; resolveHost; codex-usage 1 ms flake).

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

server/__tests__/tmux.test.js

@@ -19,6 +19,21 @@ describe("tmux wrapper", () => {
     assert.equal(tmux.hasSession("agenthub-lane-1"), true);
   });
 
+  it("hasSession answers yes from a fresh list, and asks tmux for anything else", () => {
+    const calls = [];
+    tmux.__setExecImpl((args) => {
+      calls.push(args[0]);
+      if (args[0] === "list-sessions") return "agenthub-lane-1\nagenthub-lane-1-2\n";
+      throw Object.assign(new Error("no session"), { status: 1 });
+    });
+    tmux.listSessions("agenthub-lane-");
+    assert.equal(tmux.hasSession("agenthub-lane-1-2"), true);
+    assert.deepEqual(calls, ["list-sessions"]); // no has-session spawn
+    // Not listed: asked for real (a pane that just died is never trusted).
+    assert.equal(tmux.hasSession("agenthub-lane-1-3"), false);
+    assert.deepEqual(calls, ["list-sessions", "has-session"]);
+  });
+
   it("hasSession returns false when execFileSync throws", () => {
     tmux.__setExecImpl(() => {
       const e = new Error("no such session");