feat(metrics): per-turn + per-step token/timing metrics bubbles

Consume [email protected] / [email protected] metrics: usage.stepId,
step-complete (ttft/decode/genTotal), done.durationMs/usage, and the
durable GET /conversations/:id/metrics endpoint.

- core/metrics: pure live-fold + durable-merge reducer; decode-rate TPS;
  head-aligned, stable placement; progressive per-step rows (each shown as
  its step ends) with the turn-total row gated on the done event.
- features/chat: store folds metric events + hydrates durable TurnMetrics;
  ChatView renders inline step bubbles + a turn-total bubble.
- app: MetricsSync HTTP effect (tolerates 404) injected into chat stores.
- scripts/live-probe: drives the metrics path; live-verified 17/17 vs bin/up.
- docs: regenerate .dispatch wire/transport mirrors to 0.4.0; glossary terms
  (turn/step metrics, TTFT, decode time, TPS, metrics bubble); trim handoff.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/features/chat/index.ts b/src/features/chat/index.ts
index 4f2091a..ae3e1f8 100644
--- a/src/features/chat/index.ts
+++ b/src/features/chat/index.ts
@@ -1,6 +1,7 @@
 export type { RenderedChunk, RenderGroup, ToolBatchEntry } from "../../core/chunks";
 export { groupRenderedChunks } from "../../core/chunks";
-export type { ChatTransport, HistorySync } from "./ports";
+export type { TurnMetricsEntry } from "../../core/metrics";
+export type { ChatTransport, HistorySync, MetricsSync } from "./ports";
 export type { ChatStore, ChatStoreDependencies } from "./store.svelte";
 export { createChatStore } from "./store.svelte";
 export { default as ChatView } from "./ui/ChatView.svelte";