fix: address PR review feedback

Address all reviewer comments from PR #387:

1. ✅ Add unit tests for annotations (tests/server/test_annotations.py)
   - 10 comprehensive test functions validating all annotation patterns
   - Tests for titles, read-only, destructive, idempotent operations
   - Validates specific ADR-017 decisions (webdav write, semantic search)
   - Cross-category consistency checks

2. ✅ Fix nc_webdav_write_file idempotency classification
   - Changed from idempotentHint=False to idempotentHint=True
   - Rationale: Uses HTTP PUT without version control
   - Writing same content to same path = same end state (idempotent)

3. ✅ Fix semantic search openWorldHint inconsistency
   - Changed from openWorldHint=False to openWorldHint=True
   - Rationale: Consistent with other Nextcloud tools
   - Nextcloud is external to MCP server (indexed data is implementation detail)

4. ✅ Update ADR-017 with resolved decisions
   - Converted Open Questions to Resolved Questions
   - Added detailed rationale for webdav write and semantic search
   - Updated status from Proposed to Implemented
   - Added decision timeline with dates

5. ✅ Add MCP Tool Annotations guidelines to CLAUDE.md
   - Comprehensive section with code examples for all patterns
   - Key principles documented (idempotency, destructive, open world)
   - References ADR-017 for detailed rationale

All OAuth tools verified to have proper annotations (oauth_tools.py lines 686-751).

nextcloud_mcp_server/server/semantic.py

@@ -39,7 +39,7 @@ def configure_semantic_tools(mcp: FastMCP):
         title="Semantic Search",
         annotations=ToolAnnotations(
             readOnlyHint=True,  # Search doesn't modify data
-            openWorldHint=False,  # Searches only indexed Nextcloud data
+            openWorldHint=True,  # Queries external Nextcloud service
         ),
     )
     @require_scopes("semantic:read")