feat(routing): cost-tiered complexity routing + saved presets (#656)

The 08-31 lever: model_assignments gains one compound rung —
AGENT_SLUG > ROLE('{role}:{complexity}') > ROLE > GLOBAL — so a
low-complexity task can route to a cheaper tier while coordinators stay
pinned. Structurally opt-in: zero rows means byte-identical routing
(pinned by a named test across every precedence case), the cost_tiered
apply-mode (seeds developer:low→haiku) is reachable only from the
explicit PM-gated endpoint — verified no startup path can apply it.
Overrides are downgrade-only (input-price comparator), allowlisted to
{developer, qa, documenter} — cell_pm excluded per the org's own
coordinator definition and its documented weak-model incidents — and
validated at write time (disabled/unconfigured provider rejected with
remediation; cross-provider-family overrides warn explicitly).

Per adversarial review: the four mode-switch applies now spare compound
rows exactly like agent pins (the 2026-07-17 unscoped-wipe class, new
victim, same fix extended via one shared wipe helper) with panel cache
invalidation + truthful confirm dialogs; preset apply validates the
entire payload BEFORE the wipe (validate-all-first), with a savepoint
crash test proving rollback.

Presets (CEO request): routing_presets table (migration 082) snapshots
the full mix — mode, per-agent overrides, complexity rows — with
save/apply/delete endpoints and a panel preset bar; applying skips
since-removed models with per-entry notes, never silently.

Task complexity threads task_id through _resolve_agent_route at both
call sites; taskless spawns unchanged. 235 backend + 23 panel tests.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/runtime/test_parked_spawn_shortcut.py

@@ -47,7 +47,7 @@ def _wire(monitor: dict[str, Any]) -> Any:
     async def _git_context(_gc: Any, _tid: str | None) -> None:
         return None
 
-    async def _route(_aid: str) -> Any:
+    async def _route(_aid: str, _tid: str | None = None) -> Any:
         monitor["route_calls"] += 1
         return SimpleNamespace(
             provider_type=SimpleNamespace(value="anthropic"),