feat(talk): add MCP integration for Nextcloud Talk (spreed)

Adds 6 MCP tools so an LLM can read a user's Talk conversations and
post messages on their behalf, addressing the "read my chats and reply"
use case from issue #720:

  - talk_list_conversations
  - talk_get_conversation
  - talk_get_messages
  - talk_list_participants
  - talk_send_message    (auto-attaches a referenceId for retry dedup)
  - talk_mark_as_read

Edit/delete messages, reactions, threads, and call/session ops are
intentionally out of scope for this first PR.

The TalkClient also exposes create_conversation/delete_conversation
for the integration test fixture; these are not registered as MCP
tools. A post-installation hook enables spreed in the docker dev env
so the integration suite has a real Talk backend to talk to.

Closes #720

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

nextcloud_mcp_server/server/__init__.py

@@ -12,6 +12,7 @@ from .notes import configure_notes_tools
 from .semantic import configure_semantic_tools
 from .sharing import configure_sharing_tools
 from .tables import configure_tables_tools
+from .talk import configure_talk_tools
 from .webdav import configure_webdav_tools
 
 # Canonical mapping of app name → tool registration function.
@@ -29,6 +30,7 @@ AVAILABLE_APPS: dict[str, Callable[[FastMCP], None]] = {
     "cookbook": configure_cookbook_tools,
     "deck": configure_deck_tools,
     "news": configure_news_tools,
+    "talk": configure_talk_tools,
 }
 
 __all__ = [
@@ -43,5 +45,6 @@ __all__ = [
     "configure_semantic_tools",
     "configure_sharing_tools",
     "configure_tables_tools",
+    "configure_talk_tools",
     "configure_webdav_tools",
 ]