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

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

@@ -2,9 +2,9 @@
  * AniWorld - Context Menu Component
  *
  * Right-click context menu for anime series cards.
- * Provides quick access to edit metadata.
+ * Provides quick access to NFO diagnostics.
  *
- * Dependencies: ui-utils.js, edit-modal.js
+ * Dependencies: ui-utils.js
  */
 
 var AniWorld = window.AniWorld || {};
@@ -67,10 +67,6 @@ AniWorld.ContextMenu = (function() {
         menuElement = document.createElement('div');
         menuElement.className = 'context-menu';
         menuElement.innerHTML = `
-            <div class="context-menu-item" data-action="edit">
-                <i class="fa-solid fa-pen-to-square"></i>
-                <span>Edit Metadata</span>
-            </div>
             <div class="context-menu-item" data-action="nfo-diagnostics">
                 <i class="fa-solid fa-file-circle-check"></i>
                 <span>NFO Diagnostics</span>
@@ -100,13 +96,6 @@ AniWorld.ContextMenu = (function() {
         menuElement.style.top = posY + 'px';
 
         // Attach action handlers
-        menuElement.querySelector('[data-action="edit"]').addEventListener('click', function() {
-            hide();
-            if (AniWorld.EditModal) {
-                AniWorld.EditModal.open(currentSeriesKey);
-            }
-        });
-
         // NFO Diagnostics - opens the full NFO settings page
         menuElement.querySelector('[data-action="nfo-diagnostics"]').addEventListener('click', function() {
             hide();