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>

alembic/versions/082_routing_presets.py

@@ -0,0 +1,48 @@
+"""Routing presets — named, full snapshots of the AI-routing state.
+
+Lets an operator save the current routing state (mode + every
+`model_assignments` row: GLOBAL / plain ROLE / compound ROLE(":"complexity)
+cost-tier overrides / AGENT_SLUG pins) under a name and re-apply it later in
+one call, instead of re-picking every per-agent Select. ``payload`` mirrors
+exactly what ``GET /providers`` + ``GET /providers/complexity-overrides``
+already serve, so a preset is "what the card currently shows" — see
+``ModelRoutingService.save_routing_preset`` / ``apply_routing_preset``
+(roboco/services/llm.py). Pure additive new table; no backfill, no data
+migration — applying a preset is the only thing that ever mutates
+``model_assignments`` as a side effect, and only on an explicit call.
+
+Revision ID: 082_routing_presets
+Revises: 081_doctrine_version
+Create Date: 2026-07-23
+"""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+revision = "082_routing_presets"
+down_revision = "081_doctrine_version"
+branch_labels: dict[str, str] | None = None
+depends_on: dict[str, str] | None = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "routing_presets",
+        sa.Column("id", sa.UUID(as_uuid=True), primary_key=True),
+        sa.Column("name", sa.String(length=100), nullable=False),
+        sa.Column("payload", postgresql.JSONB(), nullable=False),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.text("now()"),
+        ),
+        sa.UniqueConstraint("name", name="uq_routing_presets_name"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("routing_presets")