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/models/anime.py

@@ -10,15 +10,11 @@ Note on identifiers:
 """
 from __future__ import annotations
 
-import re
 from datetime import datetime
 from typing import List, Optional
 
 from pydantic import BaseModel, Field, HttpUrl, field_validator
 
-# Regex pattern for valid series keys (URL-safe, lowercase with hyphens)
-KEY_PATTERN = re.compile(r'^[a-z0-9][a-z0-9-]*[a-z0-9]$|^[a-z0-9]$')
-
 
 class EpisodeInfo(BaseModel):
     """Information about a single episode."""
@@ -83,30 +79,6 @@ class AnimeSeriesResponse(BaseModel):
         return v
 
 
-class AnimeMetadataUpdate(BaseModel):
-    """Request model for updating anime metadata (key, tmdb_id, tvdb_id)."""
-
-    key: Optional[str] = Field(None, description="New series key (URL-safe, lowercase)")
-    tmdb_id: Optional[int] = Field(None, ge=1, description="TMDB ID (positive integer)")
-    tvdb_id: Optional[int] = Field(None, ge=1, description="TVDB ID (positive integer)")
-
-    @field_validator('key', mode='before')
-    @classmethod
-    def validate_key_format(cls, v: Optional[str]) -> Optional[str]:
-        """Validate key is URL-safe lowercase with hyphens only."""
-        if v is None:
-            return v
-        v = v.strip().lower()
-        if not v:
-            raise ValueError("Key cannot be empty")
-        if not KEY_PATTERN.match(v):
-            raise ValueError(
-                "Key must contain only lowercase letters, numbers, and hyphens. "
-                "Cannot start or end with a hyphen."
-            )
-        return v
-
-
 class SearchRequest(BaseModel):
     """Request payload for searching series."""