feat(oidc): Enabled toggle on OIDCProvider (MED-9)

Audit 2026-05-10 Fix 13 Phase B — close MED-9. MED-4/5/6/7 deferred to v3.

MED-9: ship the OIDCProvider.Enabled boolean. Pre-fix, the only way
to take a provider offline during an incident was DELETE, which
breaks active user_oidc_provider FK references and orphans any
session that minted under the provider. Post-fix:

  - Migration 000042 adds enabled BOOLEAN NOT NULL DEFAULT TRUE.
    Default-true means existing pre-migration rows are all enabled
    post-deploy; no breaking-change window.
  - internal/auth/oidc/domain/types.go::OIDCProvider.Enabled ships
    the domain field with JSON tag 'enabled'.
  - Repository read/write paths (List, Get, GetByName, Create, Update)
    all carry the column.
  - internal/auth/oidc/service.go::HandleAuthRequest rejects with
    the new ErrProviderDisabled sentinel when cfgRow.Enabled=false.
  - cmd/server/main.go::oidcProvidersListAdapter.List filters
    disabled providers before constructing OIDCProviderInfo so the
    LoginPage's 'Sign in with X' buttons never render for offline
    IdPs.
  - Defense-in-depth: the ErrProviderDisabled service-layer check
    is the guard for direct API / MCP / CLI callers that bypass the
    GUI.

Regression test: internal/auth/oidc/provider_enabled_test.go warms
the entry cache via a successful HandleAuthRequest, flips
cfgRow.Enabled=false on the cached entry, then asserts the next call
returns ErrProviderDisabled (errors.Is). Test fixtures (newValidProvider,
makeProvider) updated to set Enabled: true so existing tests stay
green.

Operators can toggle Enabled today via the existing PUT
/api/v1/auth/oidc/providers/{id} body field. A dedicated GUI
toggle on OIDCProviderDetailPage and a single-purpose PUT-just-enabled
endpoint are deferred to the v3 GUI-polish bundle — the load-bearing
wire is in place now.

MED-4 (GUI advanced fields on edit), MED-5 (POST .../test endpoint
+ button), MED-6 (JWKS auto-refresh on cache-miss), MED-7 (JWKS
health endpoint + GUI panel): DEFERRED to v3 with explicit
annotations in the audit doc. Workarounds: MED-4 fields are
PUT-editable via curl/MCP; MED-5 → call refresh post-create;
MED-6 → call refresh manually on key rotation.

Refs: cowork/auth-bundles-audit-2026-05-10.md MED-4, MED-5, MED-6,
      MED-7, MED-9
Spec: cowork/auth-bundles-fixes-2026-05-10/13-med-bundle.md Phase B

internal/auth/oidc/provider_enabled_test.go

@@ -0,0 +1,39 @@
+package oidc
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+// Audit 2026-05-10 MED-9 closure — pin the disabled-provider behavior.
+// HandleAuthRequest must reject pre-login creation with
+// ErrProviderDisabled when the operator has flipped Enabled=false. The
+// LoginPage's AuthInfo provider list filters disabled providers at the
+// adapter (cmd/server/main.go::oidcProvidersListAdapter.List) so the
+// button doesn't render in the first place; ErrProviderDisabled is the
+// defense-in-depth guard for direct API / MCP / CLI callers.
+
+func TestService_HandleAuthRequest_DisabledProvider_RejectsWithErrProviderDisabled(t *testing.T) {
+	mockIdP := newMockIdP(t)
+	svc, _ := newServiceWithProvider(t, mockIdP.URL(), "op-disabled")
+
+	// Warm the entry cache via a successful HandleAuthRequest (this runs
+	// real discovery against mockIdP), then flip cfgRow.Enabled to false
+	// to simulate the operator toggling the provider offline. The next
+	// HandleAuthRequest hits the disabled-check before the cached entry
+	// is reused.
+	if _, _, _, err := svc.HandleAuthRequest(context.Background(), "op-disabled"); err != nil {
+		t.Fatalf("warm HandleAuthRequest: %v", err)
+	}
+	if entry, ok := svc.cache["op-disabled"]; ok && entry.cfgRow != nil {
+		entry.cfgRow.Enabled = false
+	} else {
+		t.Fatal("expected cache entry for op-disabled after warmup")
+	}
+
+	_, _, _, err := svc.HandleAuthRequest(context.Background(), "op-disabled")
+	if !errors.Is(err, ErrProviderDisabled) {
+		t.Errorf("HandleAuthRequest(disabled provider) err = %v; want ErrProviderDisabled", err)
+	}
+}