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.

crates/cm-api/src/routes/structure.rs

@@ -210,6 +210,58 @@ pub async fn orphan_counts(
     }))
 }
 
+/// `POST /api/structure/ensure-chain` — guarantee the workspace has an
+/// org + company chain and return coordinates for it. Idempotent: reuses
+/// existing rows when present, creates placeholder ones otherwise.
+/// Wizards call this before creating a team so first-team-in-a-fresh-
+/// workspace lands under real parents instead of synthesized scaffolding.
+#[derive(Deserialize, Default)]
+pub struct EnsureChainRequest {
+    /// Placeholder name used only if we have to CREATE the org.
+    #[serde(default)]
+    pub fallback_org_name: Option<String>,
+    /// Placeholder name used only if we have to CREATE the company.
+    #[serde(default)]
+    pub fallback_company_name: Option<String>,
+}
+#[derive(Serialize)]
+pub struct EnsuredChainOut {
+    pub org_id: String,
+    pub company_id: String,
+    /// `true` when either row was freshly created by this call.
+    pub created: bool,
+}
+pub async fn ensure_chain(
+    State(state): State<AppState>,
+    Authed(user): Authed,
+    Json(body): Json<EnsureChainRequest>,
+) -> Result<Json<EnsuredChainOut>, ApiError> {
+    let org_name = body
+        .fallback_org_name
+        .as_deref()
+        .map(str::trim)
+        .filter(|s| !s.is_empty())
+        .unwrap_or("My Workspace");
+    let company_name = body
+        .fallback_company_name
+        .as_deref()
+        .map(str::trim)
+        .filter(|s| !s.is_empty())
+        .unwrap_or("General");
+    let r = cm_db::repo::structure_reify::ensure_chain(
+        &state.pool,
+        user.workspace_id,
+        org_name,
+        company_name,
+    )
+    .await?;
+    Ok(Json(EnsuredChainOut {
+        org_id: r.org_id.to_string(),
+        company_id: r.company_id.to_string(),
+        created: r.created,
+    }))
+}
+
 /// `POST /api/structure/reify-orphans` — create a real org+company+team
 /// chain with the provided names and re-parent every orphan into it, all
 /// in one transaction. Returns the freshly-created ids so the client can