docs(auth): document AuthCapabilitiesController + login routing

.claude/rules/app-classes.md

@@ -112,6 +112,12 @@ Env-scoped read-path controllers (`AlertController`, `AlertRuleController`, `Ale
 - `DatabaseAdminController` — GET `/api/v1/admin/database/**` (conditional on `infrastructureendpoints` flag).
 - `ServerMetricsAdminController` — `/api/v1/admin/server-metrics/**`. GET `/catalog`, GET `/instances`, POST `/query`. Generic read API over the `server_metrics` ClickHouse table so SaaS dashboards don't need direct CH access. Delegates to `ServerMetricsQueryStore` (impl `ClickHouseServerMetricsQueryStore`). Visibility matches ClickHouse/Database admin: `@ConditionalOnProperty(infrastructureendpoints, matchIfMissing=true)` + class-level `@PreAuthorize("hasRole('ADMIN')")`. Validation: metric/tag regex `^[a-zA-Z0-9._]+$`, statistic regex `^[a-z_]+$`, `to - from ≤ 31 days`, stepSeconds ∈ [10, 3600], response capped at 500 series. `IllegalArgumentException` → 400. `/query` supports `raw` + `delta` modes (delta does per-`server_instance_id` positive-clipped differences, then aggregates across instances). Derived `statistic=mean` for timers computes `sum(total|total_time)/sum(count)` per bucket.
 
+### Auth (flat)
+
+- `UiAuthController` — `/api/v1/auth` (login, refresh, me). Local username/password against env-var admin or DB BCrypt hash. Lockout after 5 failed attempts.
+- `OidcAuthController` — `/api/v1/auth/oidc` (config, callback). Code → token exchange. Roles via custom JWT claim, claim mapping rules, or default roles.
+- `AuthCapabilitiesController` — `GET /api/v1/auth/capabilities` (unauthenticated). Reports `{oidc:{enabled, providerName, primary}, localAccounts:{enabled, adminRecoveryOnly}}` so the SPA renders the login page deterministically. `oidc.primary == oidc.enabled`; `localAccounts.adminRecoveryOnly == oidc.primary`. `providerName` is best-effort label via `OidcProviderNameDeriver` (Logto / Keycloak / Auth0 / Okta / Single Sign-On). The SPA hides the local form behind `?local` when `adminRecoveryOnly` is true.
+
 ### Other (flat)
 
 - `DetailController` — GET `/api/v1/executions/{executionId}` + processor snapshot endpoints.