feat: WP-0003 — RoutingPolicy (FR-2) and HTTP serve mode (FR-1)

FR-2 RoutingPolicy:
- RoutingPolicy + RoutingRule dataclasses in llm_connect/routing.py
- resolve(task_type, estimated_cost_per_1k=None) with cost-cap fallback
- Exported from llm_connect.__init__; contract doc at contracts/functional/routing-policy.md
- 11 tests covering rule match, cost-cap, fallback, unknown type, no-match

FR-1 HTTP serve mode:
- LLMServer in llm_connect/server.py (stdlib http.server, zero extra deps)
- POST /execute + GET /health; CLI via python -m llm_connect.server
- [server] optional-dep group added to pyproject.toml
- Contract doc at contracts/functional/server.md
- 9 tests: health, round-trip, 400/404/500 errors, config forwarding
- Added "mock" provider to factory for CLI default

All 101 tests pass.

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

contracts/functional/routing-policy.md

@@ -0,0 +1,53 @@
+# Contract: RoutingPolicy
+
+**layer:** Functional  
+**maturity:** Beta  
+**module:** `llm_connect.routing`  
+**since:** WP-0003
+
+## Purpose
+
+Route logical task types to concrete `LLMAdapter` instances based on a
+prioritised rule list, with optional per-rule cost-cap fallback.
+
+## Public surface
+
+```python
+@dataclass
+class RoutingRule:
+    task_type: str
+    prefer: LLMAdapter
+    max_cost_per_1k: Optional[float] = None   # USD per 1 000 tokens
+    fallback: Optional[LLMAdapter] = None
+
+@dataclass
+class RoutingPolicy:
+    rules: List[RoutingRule] = field(default_factory=list)
+    default: Optional[LLMAdapter] = None
+
+    def resolve(
+        self,
+        task_type: str,
+        estimated_cost_per_1k: Optional[float] = None,
+    ) -> LLMAdapter: ...
+```
+
+## Invariants
+
+1. Rules are evaluated in list order; the first rule whose `task_type` matches wins.
+2. When `estimated_cost_per_1k` is supplied and a matching rule has `max_cost_per_1k` set:
+   - If `estimated_cost_per_1k > max_cost_per_1k` **and** `fallback is not None` → return `fallback`.
+   - Otherwise → return `prefer` (no fallback configured or cost within cap).
+3. When no rule matches and `default is not None` → return `default`.
+4. When no rule matches and `default is None` → raise `LookupError`.
+5. `resolve()` never mutates policy state.
+
+## Error contract
+
+| Condition | Exception |
+|-----------|-----------|
+| No matching rule, no default | `LookupError` |
+
+## Known consumers
+
+- `inter-hub` (IHUB-WP-0012 Phase 11): uses `RoutingPolicy` to select federation adapters per task class.