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>

client/src/components/Sagi/sagi.css

@@ -1,8 +1,12 @@
 /**
  * sagi.css - animations + mood expressions for the Sagi companion.
  * Colors mirror the app's theme tokens (accent #6366f1/#818cf8, surface scale)
- * with warm pink accents (ears, cheeks, nose) for cuteness. All continuous
- * motion is disabled under [data-reduced="1"] and prefers-reduced-motion.
+ * with warm pink accents (ears, cheeks, nose) for cuteness. No mood animates
+ * forever: each plays a few cycles when the mood begins and then rests — an
+ * infinite animation makes the browser draw a new frame 60 times a second for
+ * as long as the page is open (the drop-shadow filter re-rendered each time),
+ * which made the whole desktop stutter. All motion is disabled under
+ * [data-reduced="1"] and prefers-reduced-motion.
  * Transform origins are the delicate part - see the comments on .sagi-avatar
  * and .sagi-eye-blink for which reference box each one resolves against.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
@@ -206,20 +210,20 @@
 
 /* idle: gentle breathing + occasional blink */
 .sagi-avatar[data-mood="idle"] {
-  animation: sagi-breathe 4s ease-in-out infinite;
+  animation: sagi-breathe 4s ease-in-out 0s 3;
 }
 /* Blink lives on the inner group so it never overrides the outer group's
    eye-tracking translate (which would freeze the eyes - see the CSS-blink
    note in SagiAvatar.tsx). */
 .sagi-avatar[data-mood="idle"] .sagi-eye-blink {
-  animation: sagi-blink 5s ease-in-out infinite;
+  animation: sagi-blink 5s ease-in-out 0s 3;
 }
 /* happy: whole-mascot bob + twinkling sparkle */
 .sagi-avatar[data-mood="happy"] {
   animation: sagi-bob 0.5s ease-in-out 0s 4;
 }
 .sagi-avatar[data-mood="happy"] .sagi-sparkle {
-  animation: sagi-sparkle-twinkle 0.9s ease-in-out infinite;
+  animation: sagi-sparkle-twinkle 0.9s ease-in-out 0s 4;
   transform-origin: 797px 274px; /* sparkle centre, mascot 1050,380 */
 }
 /* worried: alarmed shake */
@@ -228,19 +232,19 @@
 }
 /* stuck: slow, drooping breathe (fatigued) */
 .sagi-avatar[data-mood="stuck"] {
-  animation: sagi-droop 2.4s ease-in-out infinite;
+  animation: sagi-droop 2.4s ease-in-out 0s 3;
 }
 /* thinking: rocking head tilt */
 .sagi-avatar[data-mood="thinking"] {
-  animation: sagi-rock 1.8s ease-in-out infinite;
+  animation: sagi-rock 1.8s ease-in-out 0s 4;
 }
 /* watching: attentive sway while a session is live */
 .sagi-avatar[data-mood="watching"] {
-  animation: sagi-sway 3.2s ease-in-out infinite;
+  animation: sagi-sway 3.2s ease-in-out 0s 3;
 }
 /* sleeping: slow breathe, droop */
 .sagi-avatar[data-mood="sleeping"] {
-  animation: sagi-breathe 5s ease-in-out infinite;
+  animation: sagi-breathe 5s ease-in-out 0s 3;
 }
 
 /* ── reduced motion: kill all continuous animation ── */
@@ -339,7 +343,7 @@
   align-items: center;
   justify-content: center;
   border: 2px solid #0c0c14;
-  animation: sagi-error-pulse 1.2s ease-in-out infinite;
+  animation: sagi-error-pulse 1.2s ease-in-out 0s 5;
 }
 .sagi-bubble {
   max-width: 16rem;
@@ -375,7 +379,7 @@
 /* An uploaded still image has no frames of its own: it bobs, faster while an
    agent works and slower asleep. A Codex spritesheet animates by its frames. */
 .sagi-pet-image {
-  animation: sagi-pet-bob 2.6s ease-in-out infinite;
+  animation: sagi-pet-bob 2.6s ease-in-out 0s 3;
   -webkit-user-drag: none;
 }
 .sagi-pet-image[data-mood="thinking"] {