structure polish: post-reify nav + ensure-chain + TeamWizard auto-parent

Two small quality-of-life fixes on top of the reify commit:

Post-reify navigation
  OrphanMigrationDialog already returned team_id in its result;
  Dashboard now pushes /?team=<team_id> before router.refresh() so
  the user lands on the freshly-materialized team and sees exactly
  where their agents just moved. Previously they had to hunt for it
  in the newly-rebuilt sidebar.

Wizard auto-materialize (POST /api/structure/ensure-chain)
  cm-db: ensure_chain(pool, ws, fallback_org, fallback_company) —
    fast path returns coordinates of the first org+company already
    bound in this workspace (workspace's oldest org, oldest company
    under it). Slow path inserts a new org+company with the
    fallback names ("My Workspace" / "General") + binds them via
    org_companies. Returns { org_id, company_id, created }. Small
    txn — leaves the workspace consistent whether it was already
    wired or not.
  cm-api: POST /api/structure/ensure-chain accepts optional
    fallback_org_name and fallback_company_name in the body (trimmed,
    else default). Returns the ids.
  CreateTeamRequest gains an optional attach_to_company_id. When
    set, after build_team() completes, we look up the company
    (workspace ownership check enforced by companies::get), count
    its existing teams for a stable n_i node id, and insert a
    company_teams binding — so the team lands under the parent
    atomically instead of a follow-up round-trip.
  TeamWizard now calls ensure-chain before POST /api/teams and
    passes the returned company_id in attach_to_company_id. Both
    calls are best-effort — if ensure-chain fails (network etc.)
    we still try to create the team, and the migration dialog stays
    available as the fallback UX. Wizard flow now: fresh workspace's
    first team is fully wired from the moment it appears in the
    tree — no synthetic "My Workspace" scaffolding ever gets
    rendered around it.

The Team/Company create paths not touched here (create_team_from_claws,
company create, org create, MasterPlannerModal scaffold) still
work as before — they just won't auto-parent yet. Later commits
can wire them the same way.

.sqlx/query-4cccf6d1f49e67d752fdd54dfab52c56a80381374b03dc7c4c7cd4d86e976080.json

@@ -0,0 +1,28 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "SELECT oc.org_id AS org_id, oc.company_id AS company_id\n           FROM org_companies oc\n           JOIN orgs o ON o.id = oc.org_id\n          WHERE o.workspace_id = $1\n          ORDER BY o.created_at\n          LIMIT 1",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "org_id",
+        "type_info": "Uuid"
+      },
+      {
+        "ordinal": 1,
+        "name": "company_id",
+        "type_info": "Uuid"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Uuid"
+      ]
+    },
+    "nullable": [
+      false,
+      false
+    ]
+  },
+  "hash": "4cccf6d1f49e67d752fdd54dfab52c56a80381374b03dc7c4c7cd4d86e976080"
+}