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>

docs/HOOKS.md

@@ -182,7 +182,7 @@ npm run install-hooks
 > (Escape hatch for running Claude Code *inside* the same container:
 > `AGENTHUB_ALLOW_CONTAINER_HOOKS=1 npm run install-hooks`.)
 
-For each of the eight hook types it adds one entry to `~/.claude/settings.json` that runs the handler with the type as its argument; the five tool/turn hooks (`PreToolUse`, `PostToolUse`, `Stop`, `SubagentStop`, `Notification`) carry `"matcher": "*"`. Entries that are not AgentHub's are left alone. There is nothing else to install — Claude Code runs `scripts/hook-handler.js` directly.
+For each of the eight hook types it adds one entry to `~/.claude/settings.json` that runs the handler with the type as its argument; the five tool/turn hooks (`PreToolUse`, `PostToolUse`, `Stop`, `SubagentStop`, `Notification`) carry `"matcher": "*"`. `PreToolUse` and `PostToolUse` also carry `"async": true` (`ASYNC_HOOKS` in `scripts/install-hooks.js`, and the same in `.claude-plugin/plugin.json`): they fire around every tool call, and Claude Code waits for a synchronous hook before going on — each a Node start of 0.1–0.2 s, so ~0.4 s added to every tool call. The handler only reports (it prints nothing and decides nothing), so nothing is lost by not waiting; the rarer hooks stay synchronous so a turn's start and end reach the dashboard in order. Entries that are not AgentHub's are left alone. There is nothing else to install — Claude Code runs `scripts/hook-handler.js` directly.
 
 ```json
 {
@@ -191,7 +191,7 @@ For each of the eight hook types it adds one entry to `~/.claude/settings.json`
       {
         "matcher": "*",
         "hooks": [
-          { "type": "command", "command": "node \"/path/to/agenthub/scripts/hook-handler.js\" PreToolUse" }
+          { "type": "command", "command": "node \"/path/to/agenthub/scripts/hook-handler.js\" PreToolUse", "async": true }
         ]
       }
     ],