feat(chat): opt-in live TTFT / tok/s chip in the composer

[123ada11f]

Supersedes #2713 (author @monikalnbo) — that PR has been CONFLICTING since 2026-08-23.

What this is

A rebase of #2713 onto current main, keeping the original author on the commit and the original intent intact: an opt-in chip inside the composer showing TTFT and a rolling tok/s estimate while a reply streams, driven by a new packages/client/src/utils/hermes/stream-metrics.ts (2-second sliding window over streamed deltas, estimated tokens from chunk text).

What I changed on top of the original

• ChatInput.vue props block conflicted with main — kept main's initialText / persistDraft defaults and the new showStreamSpeed prop.
• Dropped a stale noteRunStart(sid) call in stores/hermes/chat.ts: no such export exists in stream-metrics.ts, so it would fail vue-tsc. noteStreamStart(sid) on the next line already records the run-issue moment that the TTFT clock measures from.

Net: +180 / -0 across 15 files (was +181/-0 before removing the stale call). Purely additive — nothing from main is deleted.

Verification

• 3-way merge (base → main → PR head) done locally with git merge-file; only the ChatInput.vue props block conflicted, and no conflict markers remain anywhere in the change set.
• The result was diffed against main and stays additive in shape, matching the original PR's footprint.
• Upstream CI is the authoritative check; local type-check notes will follow in a comment (this box has Node 22 while the repo declares >=23).

Context

Issue #3178 asks for exactly this in the chat UI and notes that the official desktop app already surfaces avg_tps / cache_hit_pct from the TUI gateway while Studio's web UI shows neither. For anyone who wants it today without rebuilding, there is also a non-invasive local overlay (inject a script, or CDP runtime injection — no source changes): https://github.com/123ada11f/ekko-studio-tokps ; anything useful from it (e.g. reading GET /api/studio/sessions/:id for real token counts) can be folded in here instead.

[123ada11f]

本地验证补充（这台机器的实际情况，供参考）：

• 合并干净：三方合并（PR base → main → PR head）在本地用 git merge-file 做，只有 ChatInput.vue 的 props 块冲突，按"两边都保留"解决（initialText/persistDraft + showStreamSpeed）；改动集里已确认没有冲突标记。
• 仍是纯新增：相对 main 为 +180/-0、15 文件（移除那行 stale 的 noteRunStart(sid) 之前是 +181/-0）。
• 语法级检查已过（node --experimental-strip-types --check）：
  packages/client/src/utils/hermes/stream-metrics.ts（新增）、stores/hermes/chat.ts、
  ChatInput.vue 的 <script setup> 块、i18n/locales/{zh,en,ja}.ts。
• 完整 vue-tsc 没能跑：npm ci 两次都因网络中断（ECONNRESET，本机需走代理）失败，依赖装到 ~815 MB 时断开；这台机器是 Node 22，而仓库声明 >=23。
• 上面的 Build / Playwright 两个 workflow 已触发但状态是 action_required —— fork 来的 PR 需要维护者批准才会运行。

批准后如果 vue-tsc 报错，把日志贴过来，我立刻跟进修。

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追加：本机能做的语法层验证已跑过（依赖仍装不上）

• node --experimental-strip-types --check 全部通过：新增的 packages/client/src/utils/hermes/stream-metrics.ts、改动后的 stores/hermes/chat.ts、ChatInput.vue 的 <script setup> 块，以及抽查的 i18n/locales/{zh,en,ja}.ts。
• npm ci 两次都在约 815 MB 处 ECONNRESET 失败（本机必须走代理），因此 vue-tsc 仍未能本地执行；这台机器是 Node 22 而仓库要求 >=23。
• 上面的 Build / Playwright 仍为 action_required，等维护者批准后即为权威验证。