feat: Complete Phase 5 - Instrument all 93 MCP tools

Applied @instrument_tool decorator to all 86 remaining tools
across 8 server files.

Instrumented files:
- calendar.py: 16 tools
- contacts.py: 7 tools
- deck.py: 25 tools
- webdav.py: 11 tools
- tables.py: 6 tools
- sharing.py: 5 tools
- cookbook.py: 13 tools
- semantic.py: 3 tools

Total: 93 tools instrumented (7 in notes.py + 86 in other files)

These metrics populate:
- MCP Tool Calls panel (by tool name and status)
- MCP Tool Duration panel (histogram)
- MCP Tool Errors panel (by tool name and error type)

This completes PR #295 - All 5 phases of metrics instrumentation done:
✅ Phase 1: Queue size metrics (2 locations)
✅ Phase 2: Health checks (1 location)
✅ Phase 3: Database operations (3 methods)
✅ Phase 4: OAuth token metrics (3 locations)
✅ Phase 5: MCP tool metrics (93 tools)

All 34 dashboard panels now have data sources.

nextcloud_mcp_server/server/sharing.py

@@ -6,6 +6,7 @@ from mcp.server.fastmcp import Context, FastMCP
 
 from nextcloud_mcp_server.auth import require_scopes
 from nextcloud_mcp_server.context import get_client
+from nextcloud_mcp_server.observability.metrics import instrument_tool
 
 
 def configure_sharing_tools(mcp: FastMCP):
@@ -17,6 +18,7 @@ def configure_sharing_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("sharing:write")
+    @instrument_tool
     async def nc_share_create(
         path: str,
         share_with: str,
@@ -56,6 +58,7 @@ def configure_sharing_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("sharing:write")
+    @instrument_tool
     async def nc_share_delete(share_id: int, ctx: Context) -> str:
         """Delete a share by its ID.
 
@@ -75,6 +78,7 @@ def configure_sharing_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("sharing:write")
+    @instrument_tool
     async def nc_share_get(share_id: int, ctx: Context) -> str:
         """Get information about a specific share.
 
@@ -93,6 +97,7 @@ def configure_sharing_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("sharing:write")
+    @instrument_tool
     async def nc_share_list(
         ctx: Context, path: str | None = None, shared_with_me: bool = False
     ) -> str:
@@ -114,6 +119,7 @@ def configure_sharing_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("sharing:write")
+    @instrument_tool
     async def nc_share_update(share_id: int, permissions: int, ctx: Context) -> str:
         """Update the permissions of an existing share.