feat(api): config + role→model routing (qwen3.5 narrator default, think off)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/app/routing.py

@@ -0,0 +1,25 @@
+"""Role → model routing (charter §4/§5). Model choice is config, not law — a
+deploy, not a client patch. Read at call time so an env override needs no reimport.
+The provider abstraction (Ollama → Replicate) slots in here later (YAGNI now).
+"""
+
+from dataclasses import dataclass
+
+from . import config
+
+
+@dataclass(frozen=True)
+class RoleConfig:
+    model: str
+    options: dict
+    think: bool | None = None  # Ollama top-level `think`; None omits it
+
+
+def for_role(role: str) -> RoleConfig:
+    if role == "narrator":
+        return RoleConfig(
+            model=config.narrator_model(),
+            options={"temperature": 0.8, "top_p": 0.9, "num_predict": 300},
+            think=False,  # qwen3.x thinking OFF; harmless on non-thinking models
+        )
+    raise KeyError(f"no routing for role: {role}")