refactor: remove Edit Metadata right-click option

Removes the Edit Metadata feature from the anime context menu and
deletes all related backend/frontend code:

Backend:
- DELETE PUT /api/anime/{anime_key} endpoint
- DELETE AnimeMetadataUpdate model and KEY_PATTERN regex
- DELETE MAX_INPUT_LENGTH constant

Frontend:
- DELETE edit-modal.js component
- DELETE edit metadata modal HTML from index.html
- DELETE edit-modal.js script tag
- DELETE edit-only CSS (.edit-modal-content, .edit-section,
  .field-error, .input-error, .key-warning, .info-grid,
  .info-item, .input-with-action, .btn-fetch-tmdb, .tmdb-*)
- REMOVE 'Edit Metadata' item from context menu (NFO Diagnostics
  preserved)

Tests:
- DELETE test_anime_edit_endpoints.py
- DELETE test_edit_modal.py
- DELETE test_anime_key_rename.py

tests/frontend/test_edit_modal.py

@@ -1,115 +0,0 @@
-"""Frontend tests for the edit metadata modal HTML structure."""
-from unittest.mock import AsyncMock, Mock, patch
-
-import pytest
-from httpx import ASGITransport, AsyncClient
-
-from src.server.fastapi_app import app
-from src.server.services.auth_service import auth_service
-
-
-@pytest.fixture(autouse=True)
-def reset_auth():
-    """Reset authentication state before each test."""
-    original_hash = auth_service._hash
-    auth_service._hash = None
-    auth_service._failed.clear()
-    yield
-    auth_service._hash = original_hash
-    auth_service._failed.clear()
-
-
-@pytest.fixture
-async def client():
-    """Create an async test client."""
-    transport = ASGITransport(app=app)
-    async with AsyncClient(transport=transport, base_url="http://test") as ac:
-        yield ac
-
-
-@pytest.fixture
-async def authenticated_client(client):
-    """Create authenticated client to access index page."""
-    await client.post(
-        "/api/auth/setup",
-        json={"master_password": "TestPassword123!"}
-    )
-    response = await client.post(
-        "/api/auth/login",
-        json={"password": "TestPassword123!"}
-    )
-    token = response.json()["access_token"]
-    client.headers.update({"Authorization": f"Bearer {token}"})
-    # Set cookie for page access
-    client.cookies.set("access_token", token)
-    yield client
-
-
-class TestEditModalHtmlPresence:
-    """Tests verifying edit modal HTML elements exist in index page."""
-
-    @pytest.mark.asyncio
-    async def test_index_page_contains_edit_modal(self, authenticated_client):
-        """Verify #edit-metadata-modal exists in rendered index page."""
-        response = await authenticated_client.get("/")
-
-        # Page may redirect or require different auth for HTML pages
-        if response.status_code == 200:
-            html = response.text
-            assert 'id="edit-metadata-modal"' in html
-
-    @pytest.mark.asyncio
-    async def test_index_page_loads_context_menu_script(self, authenticated_client):
-        """Verify context-menu.js script tag is present."""
-        response = await authenticated_client.get("/")
-
-        if response.status_code == 200:
-            html = response.text
-            assert "context-menu.js" in html
-
-    @pytest.mark.asyncio
-    async def test_index_page_loads_edit_modal_script(self, authenticated_client):
-        """Verify edit-modal.js script tag is present."""
-        response = await authenticated_client.get("/")
-
-        if response.status_code == 200:
-            html = response.text
-            assert "edit-modal.js" in html
-
-    @pytest.mark.asyncio
-    async def test_modal_form_fields_present(self, authenticated_client):
-        """Verify key, tmdb_id, tvdb_id input fields exist in modal."""
-        response = await authenticated_client.get("/")
-
-        if response.status_code == 200:
-            html = response.text
-            assert 'id="edit-key"' in html
-            assert 'id="edit-tmdb-id"' in html
-            assert 'id="edit-tvdb-id"' in html
-
-    @pytest.mark.asyncio
-    async def test_nfo_repair_button_present(self, authenticated_client):
-        """Verify repair NFO button exists in modal."""
-        response = await authenticated_client.get("/")
-
-        if response.status_code == 200:
-            html = response.text
-            assert 'id="btn-repair-nfo"' in html
-
-    @pytest.mark.asyncio
-    async def test_save_button_present(self, authenticated_client):
-        """Verify save button exists in modal."""
-        response = await authenticated_client.get("/")
-
-        if response.status_code == 200:
-            html = response.text
-            assert 'id="btn-save-metadata"' in html
-
-    @pytest.mark.asyncio
-    async def test_modal_starts_hidden(self, authenticated_client):
-        """Verify modal has hidden class by default."""
-        response = await authenticated_client.get("/")
-
-        if response.status_code == 200:
-            html = response.text
-            assert 'id="edit-metadata-modal" class="modal hidden"' in html