test(e2e): add TC-E2E-003/004/005/007/008/009/010 — delete, pagination, errors, profile, theme

- test_post_deletion.py: user delete own, admin delete any, 403 for other's
- test_pagination.py: navigation across pages, boundary on last page
- test_errors.py: 404 nonexistent post, 404 for other user's draft
- test_post_lifecycle.py: draft-to-publish via edit flow
- test_post_ownership.py: user can edit own post
- test_profile_and_theme.py: profile page rendering, theme toggle with localStorage
- fix(web): remove infinite pagination for USER role (routes.py)
- fix(e2e): stabilize all publish() calls with expect_navigation
- fix(e2e): add _unique_title() to avoid slug collisions at scale
- docs: update FEATURE_POST_LIFECYCLE.md and TEST_MODEL.md coverage

tests/FEATURE_POST_LIFECYCLE.md

@@ -207,6 +207,49 @@ Covers both API use cases and web UI end-to-end flows.
   - User2 receives 404 when accessing draft directly
 - **Last Verified:** 2026-05-07
 
+### TC-E2E-003: Negative — 404 for Nonexistent Post
+- **Type:** Negative
+- **Layer:** E2E
+- **File:** `e2e/test_errors.py::test_nonexistent_post_returns_404`
+- **Preconditions:** Dev server running, `guest_page`, `user_page` fixtures
+- **Steps:**
+  1. Generate a random slug that does not exist in the database.
+  2. Navigate to `/web/posts/{fake-slug}` as guest and as authenticated user.
+- **Expected:**
+  - Error page is rendered with `data-testid="error-code"` showing `404`
+  - Both guest and user see the same 404 response
+- **Last Verified:** 2026-05-08
+
+### TC-E2E-003a: Policy — 404 for Another User's Draft
+- **Type:** Policy
+- **Layer:** E2E
+- **File:** `e2e/test_errors.py::test_other_user_draft_returns_404`
+- **Preconditions:** Dev server running, `user_page`, `user2_page`, `guest_page` fixtures
+- **Steps:**
+  1. User creates a draft post and saves it.
+  2. Extract the slug from the detail page URL.
+  3. User2 and guest navigate to `/web/posts/{slug}`.
+- **Expected:**
+  - Owner sees the draft detail with "Draft" badge (200)
+  - User2 sees 404 error page
+  - Guest sees 404 error page
+- **Last Verified:** 2026-05-08
+
+### TC-E2E-004: Positive — Delete Post via Web UI
+- **Type:** Positive
+- **Layer:** E2E
+- **File:** `e2e/test_post_deletion.py::test_user_can_delete_own_post`
+- **Preconditions:** Dev server running, `user_page` fixture
+- **Steps:**
+  1. Generate post data via `PostDataGenerator`
+  2. Open home page and click "Write a Post"
+  3. Fill form (title, content, tags) and click "Publish Post"
+  4. On post detail page, click "Delete" and accept confirm dialog
+- **Expected:**
+  - Redirect to `/web/`
+  - Post no longer appears on home page
+- **Last Verified:** 2026-05-07
+
 ## Coverage Summary
 
 | Aspect | Coverage | Notes |
@@ -214,8 +257,8 @@ Covers both API use cases and web UI end-to-end flows.
 | Create post | Unit + E2E | Both happy path and duplicate slug covered |
 | Read post (by id/slug) | Unit | E2E implicitly via detail page |
 | Update post | Unit | No dedicated E2E |
-| Delete post | Unit | No dedicated E2E |
-| Publish / Unpublish | Unit + E2E | Authz checks covered in both layers |
+| Delete post | Unit + E2E | Own-post and admin-delete covered |
+| Publish / Unpublish | Unit + E2E | Draft-to-publish flow covered via edit |
 | List posts (all filters) | Unit | Pagination arguments passed but not edge-case tested |
 | Search posts | Unit | No E2E search flow |
 
@@ -225,8 +268,11 @@ Covers both API use cases and web UI end-to-end flows.
 - [ ] TC-UNIT-024: UpdatePostUseCase — not found scenario
 - [ ] TC-UNIT-025: UpdatePostUseCase — validation error
 - [ ] TC-UNIT-026: ListPostsUseCase — pagination edge cases (page boundaries, empty page)
-- [ ] TC-E2E-003: Edit post via web UI and verify changes
-- [ ] TC-E2E-004: Delete post via web UI and verify removal
-- [ ] TC-E2E-005: Save post as draft and verify it does not appear to guests
+- [x] TC-E2E-003: 404 error page for nonexistent post
+- [x] TC-E2E-003a: Edit post via web UI and verify changes (own post)
+- [x] TC-E2E-004: Delete post via web UI and verify removal
+- [x] TC-E2E-005: Save post as draft and publish via edit, verify visibility change
 - [ ] TC-E2E-006: Search posts via web UI
-- [ ] TC-E2E-007: Pagination navigation on home page
+- [x] TC-E2E-007: Pagination navigation on home page
+- [x] TC-E2E-009: Profile page renders user info and role badge correctly
+- [x] TC-E2E-010: Theme toggle switches between light and dark with localStorage persistence