feat: add anime metadata editing and NFO diagnostics

- Add PUT /anime/{key} endpoint for updating anime key, tmdb_id, tvdb_id
- Add NFO diagnostics and repair endpoints (GET/POST /nfo/diagnostics)
- Add edit modal UI with context menu integration
- Add frontend JS modules for context-menu and edit-modal
- Add comprehensive tests for edit, rename, and NFO repair flows

src/server/models/anime.py

@@ -83,6 +83,30 @@ 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."""
 

src/server/models/nfo.py

@@ -355,3 +355,29 @@ class NFOMissingResponse(BaseModel):
         ...,
         description="List of series missing NFO"
     )
+
+
+class NfoDiagnosticsResponse(BaseModel):
+    """Response for NFO diagnostics showing missing required tags."""
+
+    has_nfo: bool = Field(..., description="Whether tvshow.nfo exists")
+    nfo_path: Optional[str] = Field(None, description="Path to NFO file if exists")
+    missing_tags: List[str] = Field(
+        default_factory=list,
+        description="List of missing required tag names"
+    )
+    required_tags: List[str] = Field(
+        default_factory=list,
+        description="All required tag names for reference"
+    )
+
+
+class NfoRepairResponse(BaseModel):
+    """Response after NFO repair attempt."""
+
+    success: bool = Field(..., description="Whether repair succeeded")
+    message: str = Field(..., description="Human-readable result message")
+    repaired_tags: List[str] = Field(
+        default_factory=list,
+        description="Tags that were missing before repair"
+    )