✨ feat(model-bank): knowledgeCutoff batch 2, metadata skill & always-visible tab bar (#15663)

* ✨ feat(model-bank): backfill knowledgeCutoff batch 2 and restore lost Anthropic values

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* 📝 docs(skills): add model-bank-metadata skill for cutoff/family backfill

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* 🐛 fix(model-bank): Claude Fable 5 belongs to the claude-mythos family

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* 💄 style(desktop): always surface the tab bar by creating a tab on first navigation

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* ♻️ refactor(model-bank): family is the product lineage (claude-opus/sonnet/haiku), not the brand

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* 🐛 fix(agent): backfill activeAgentId before paint on tab/route switches

Tab switches are plain route navigations, so leaving an agent page cleared
activeAgentId via a passive useUnmount and the next page re-set it in a
passive useEffect — the first painted frame always had no active id, flashing
a skeleton even when agentMap already cached the config. Move both the
backfill and the unmount clear to layout effects: removed-tree layout
cleanups run before new-tree layout effects in one commit, so the clear can
never wipe a freshly synced id and the id is in place before paint.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* ✨ feat(agent): surface agent config fetch errors with a retry action

isAgentConfigLoading only knows "no data yet", so a failed fetch (e.g. a 401
that SWR deliberately does not retry, with no focus revalidation inside a
single Electron window) left the agent page on a skeleton forever — only a
manual reload recovered. Record per-agent fetch errors in
agentConfigErrorMap (set by onError, cleared on data / retry), expose
currentAgentConfigError / isAgentConfigError selectors, add a
retryAgentConfigFetch action that revalidates the agent's SWR entries, and
show an error alert with a retry button above the main chat input while the
config is still missing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* 🐛 fix(ci): sync model metadata test expectations

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

locales/en-US/chat.json

@@ -15,6 +15,8 @@
   "agentBuilder.installPlugin.retry": "Retry",
   "agentBuilder.title": "Agent Builder",
   "agentBuilder.welcome": "Tell me your use case.\n\nWriting, coding, or data analysis—anything works. You own the goal and standards; I’ll break it down into collaborative, runnable Agents.",
+  "agentConfigError.retry": "Retry",
+  "agentConfigError.title": "Failed to load agent settings",
   "agentDefaultMessage": "Hi, I’m **{{name}}**. One sentence is enough.\n\nWant me to match your workflow better? Go to [Agent Settings]({{url}}) and fill in the Agent Profile (you can edit it anytime).",
   "agentDefaultMessageWithSystemRole": "Hi, I’m **{{name}}**. One sentence is enough—you're in control.",
   "agentDefaultMessageWithoutEdit": "Hi, I’m **{{name}}**. One sentence is enough—you're in control.",

locales/zh-CN/chat.json

@@ -15,6 +15,8 @@
   "agentBuilder.installPlugin.retry": "重试",
   "agentBuilder.title": "助理构建专家",
   "agentBuilder.welcome": "先说说你的使用场景吧。\n\n写作、编程、数据分析都可以——你负责目标与标准，我来帮你把想法拆成可协作、可运行的助理。",
+  "agentConfigError.retry": "重试",
+  "agentConfigError.title": "助理配置加载失败",
   "agentDefaultMessage": "你好，我是 **{{name}}**。从一句话开始就行。\n\n想让我更贴近你的工作方式：去 [助理设置]({{url}}) 补充助理档案（随时可改）",
   "agentDefaultMessageWithSystemRole": "你好，我是 **{{name}}**。从一句话开始就行——决定权在你",
   "agentDefaultMessageWithoutEdit": "你好，我是 **{{name}}**。从一句话开始就行——决定权在你",