feat(anime): rename NFO Diagnostics to Anime Settings + add edit endpoints

Replaces the read-only 'NFO Diagnostics' page with a full per-anime
Settings page reached from the right-click context menu on series cards.
Users can now view and edit key, name, folder, tmdb_id, tvdb_id and site
for each anime; changes are persisted to the DB and optionally written
back to the NFO file or used to regenerate it.

Backend
- Rename NfoDiagnosticsResponse -> NfoSettingsResponse,
  NfoSeriesDiagnostics -> NfoSeriesSettings
- Rename get_nfo_diagnostics -> get_nfo_settings,
  repair_nfo -> repair_nfo_settings
- Fix nfo.py bug: repair was calling non-existent
  update_series_nfo_status(); now uses update_nfo_status() and an
  explicit AnimeSeriesService.update(nfo_path=...)
- New endpoints on /api/anime/{key}:
    GET  /settings            -> AnimeSettingsResponse
    PUT  /settings            -> AnimeSettingsResponse
                                 (body: name/folder/tmdb_id/tvdb_id/site,
                                  options: apply_to_nfo, rename_disk)
    POST /regenerate-nfo      -> AnimeSettingsRegenerateNfoResponse
- New Pydantic models: AnimeSettingsResponse,
  AnimeSettingsUpdateRequest, AnimeSettingsRegenerateNfoResponse
- /anime/settings page route; /settings/nfo now 301-redirects to it

Frontend
- New AniWorld.AnimeSettingsManager JS module (single-page form,
  no tabs) with public API init/loadSeries/saveSettings/regenerateNfo/
  validateField/populateForm/showSaveSuccess/showError
- New anime-settings.html template + anime-settings.css
- Right-click menu: data-action 'nfo-diagnostics' replaced by
  'anime-settings' (label 'Anime Settings'), navigates to
  /anime/settings?key=...
- Library 'Open NFO Diagnostics' link renamed to 'Open Anime Settings'

Bug fix
- context-menu click handler was calling hide() BEFORE building the
  navigation URL, which cleared currentSeriesKey to null and produced
  /anime/settings?key=null. Captures the key into a local const first.
  Regression-locked by tests/frontend/unit/context_menu.test.js.

Tests
- 21 new pytest tests in tests/api/test_anime_settings_endpoints.py
  (GET/PUT/regenerate-nfo, auth, validation, nfo-repair bug regression)
- tests/api/test_nfo_endpoints.py trimmed to 6 focused tests
- 31 new Vitest unit tests for AnimeSettingsManager
- 5 new Vitest unit tests for ContextMenu (incl. source-invariant
  regression guard for the hide()-before-key bug)
- 5 new Playwright E2E tests covering right-click, direct nav,
  legacy /settings/nfo redirect, and context-menu labels
- New vitest.config.js (environment: happy-dom)

Docs
- Docs/API.md: new section 'Anime Settings Endpoints'
- Docs/CHANGELOG.md: documents the rename and the context-menu bug fix

Verified
- pytest: 27/27 (21 new + 6 trimmed nfo)
- vitest: 36/36 (31 anime-settings + 5 context-menu)
- playwright e2e: 5/5

src/server/web/static/js/index/context-menu.js

@@ -2,7 +2,7 @@
  * AniWorld - Context Menu Component
  *
  * Right-click context menu for anime series cards.
- * Provides quick access to NFO diagnostics.
+ * Provides quick access to per-anime settings.
  *
  * Dependencies: ui-utils.js
  */
@@ -67,9 +67,9 @@ AniWorld.ContextMenu = (function() {
         menuElement = document.createElement('div');
         menuElement.className = 'context-menu';
         menuElement.innerHTML = `
-            <div class="context-menu-item" data-action="nfo-diagnostics">
-                <i class="fa-solid fa-file-circle-check"></i>
-                <span>NFO Diagnostics</span>
+            <div class="context-menu-item" data-action="anime-settings">
+                <i class="fa-solid fa-gear"></i>
+                <span>Anime Settings</span>
             </div>
         `;
 
@@ -96,11 +96,13 @@ AniWorld.ContextMenu = (function() {
         menuElement.style.top = posY + 'px';
 
         // Attach action handlers
-        // NFO Diagnostics - opens the full NFO settings page
-        menuElement.querySelector('[data-action="nfo-diagnostics"]').addEventListener('click', function() {
+        // Anime Settings - opens the per-anime settings page
+        menuElement.querySelector('[data-action="anime-settings"]').addEventListener('click', function() {
+            // Capture the key BEFORE hide() clears it
+            const key = currentSeriesKey;
             hide();
-            // Navigate to NFO settings page with this series selected
-            window.location.href = '/settings/nfo?key=' + encodeURIComponent(currentSeriesKey);
+            // Navigate to anime settings page with this series selected
+            window.location.href = '/anime/settings?key=' + encodeURIComponent(key);
         });
     }