fix(p0): 實測修正 — timeout 依 benchmark 調整，_local_fallback_chain 移除雲端 Nemotron

- config.py: NEMOTRON_DIAGNOSE_TIMEOUT_SECONDS=60s (NIM 實測 11-45s + 15s buffer)
- config.py: OLLAMA_DIAGNOSE_TIMEOUT_SECONDS=200s (Ollama 實測 ~173s + 27s buffer)
- ollama.py: 新增 per-task timeout (diagnose/force_local 用 200s)
- ai_router.py: _local_fallback_chain 移除 Nemotron (NIM=雲端，不可進 local chain)
- ai_router.py: v4.2 — Option C 分情境路由正式確立

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/core/config.py

@@ -85,13 +85,16 @@ class Settings(BaseSettings):
         description="Phase 22: True=異步更新 (先推 OpenClaw), False=同步等待",
     )
     # 2026-04-04 ogt: Phase 25 P0 — DIAGNOSE Privacy-First 專用 timeout
+    # 實測依據 (2026-04-04):
+    #   NIM 雲端: 11-45s (免費 tier，偶有排隊)  → 60s timeout (45s + 15s buffer)
+    #   Ollama 本地 llama3.2:3b: ~173s 首次推理 → 200s timeout (173s + 27s buffer)
     NEMOTRON_DIAGNOSE_TIMEOUT_SECONDS: int = Field(
-        default=30,
-        description="Phase 25 P0: DIAGNOSE 任務 Nemotron timeout (秒)，比 Tool Calling 短",
+        default=60,
+        description="Phase 25 P0: 一般 DIAGNOSE 任務 NIM timeout (秒)，實測 11-45s，60s 含 buffer",
     )
     OLLAMA_DIAGNOSE_TIMEOUT_SECONDS: int = Field(
-        default=60,
-        description="Phase 25 P0: DIAGNOSE 任務 Ollama backup timeout (秒)，Ollama 較慢",
+        default=200,
+        description="Phase 25 P0: FORCE_LOCAL DIAGNOSE Ollama timeout (秒)，實測 ~173s，200s 含 buffer",
     )
 
     # ==========================================================================