feat: block self-stack lifecycle ops with UI and preflight guardrails (#1569)

* feat: block self-stack lifecycle ops with UI and preflight guardrails

Refuse update, deploy, down, stop, and delete when the stack matches Sencho's compose project.

Return 409 self_stack_protected. Expose isSelf on /statuses and disable guarded UI actions.

Add SelfStackProtectedDialog and self-managed-stack preflight warning.

Closes #1564

* fix: add missing stackSelfFlags mock to useSidebarContextMenu test

The production hook now reads stackListState.stackSelfFlags[file], but the
test mock did not include it, causing 6 tests to fail with TypeError:
Cannot read properties of undefined (reading 'web.yml').

* fix: harden self-stack protection during startup

Add a global environment preflight warning when Sencho is managed inside COMPOSE_DIR.

Align status decoration and route guards on Docker label fallback detection.

Block rollback and service-level stop on the protected self stack.

* fix: add self_stack_location to diagnostics-route expected check IDs

frontend/src/hooks/__tests__/useStackMenuItems.test.tsx

@@ -7,6 +7,7 @@ import type { StackMenuCtx } from '@/components/sidebar/sidebar-types';
 function makeCtx(overrides: Partial<StackMenuCtx> = {}): StackMenuCtx {
   return {
     stackStatus: 'running',
+    isSelfStack: false,
     canOpenApp: true,
     isBusy: false,
     isAdmin: true,
@@ -179,4 +180,10 @@ describe('useStackMenuItems', () => {
     const scheduleItem = lifecycle.items.find(i => i.id === 'schedule')!;
     expect(scheduleItem.disabled).toBeFalsy();
   });
+
+  it('disables delete for the self stack', () => {
+    const { result } = renderHook(() => useStackMenuItems('sencho.yml', makeCtx({ isSelfStack: true })));
+    const destructive = result.current.find(g => g.id === 'destructive')!;
+    expect(destructive.items[0].disabled).toBe(true);
+  });
 });