feat(deck): add file/note attachment MCP tools

Adds four tools that expose Deck card attachments via the MCP surface:
deck_attach_file, deck_attach_note, deck_list_attachments, and
deck_delete_attachment. The attach* variants share an existing Files
entry (or Notes-app note) with the card via OCS shareType=12 — same
mechanism the Deck UI's "Share from Files" picker uses, no file copy.

This replaces the prior workaround of appending bulky activity content
as Deck card comments: per-PR/per-event narrative now lives in NC Notes
and surfaces on the tracking card as a clickable attachment that opens
the original note in place.

Implementation reuses existing client methods (SharingClient.create_share,
DeckClient.get/delete_attachment, NotesClient.get_settings/get_note);
no new client code. _SHARE_TYPE_DECK is centralised with a CI-guard test
to prevent silent drift, and SharingClient.create_share's wire format is
pinned to what the Deck Vue source sends.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/models/deck.py

@@ -144,6 +144,11 @@ class DeckAttachmentExtendedData(BaseModel):
     filesize: int
     mimetype: str
     info: Dict[str, str]
+    # Populated for type="file" (Files share) attachments via FilesAppService.
+    path: Optional[str] = None
+    fileid: Optional[int] = None
+    hasPreview: Optional[bool] = None
+    permissions: Optional[int] = None
 
 
 class DeckAttachment(BaseModel):
@@ -308,3 +313,37 @@ class CardCommentOperationResponse(StatusResponse):
 
     card_id: int = Field(description="ID of the card the comment belongs to")
     comment_id: int = Field(description="ID of the affected comment")
+
+
+# Attachment Response Models
+
+
+class AttachFileResponse(BaseResponse):
+    """Response model for attaching an existing Nextcloud file to a Deck card.
+
+    The attachment is created by sharing the file with the card via the standard
+    OCS Sharing API using ``shareType=12`` (``IShare::TYPE_DECK``). The returned
+    ``attachment_id`` is the share ID, which is also the Deck attachment ID.
+    """
+
+    attachment_id: int = Field(
+        description="ID of the created attachment (share ID)",
+    )
+    card_id: int = Field(description="ID of the card the file is attached to")
+    path: str = Field(description="Path of the shared file in the user's Files")
+
+
+class ListAttachmentsResponse(BaseResponse):
+    """Response model for listing card attachments."""
+
+    results: list["DeckAttachment"] = Field(
+        description="Attachments on the card (both type='file' and type='deck_file')"
+    )
+    count: int = Field(description="Number of attachments returned")
+
+
+class AttachmentOperationResponse(StatusResponse):
+    """Response model for attachment operations that don't return data (e.g. delete)."""
+
+    card_id: int = Field(description="ID of the card the attachment belongs to")
+    attachment_id: int = Field(description="ID of the affected attachment")