feat: implement ADR-009 - refactor semantic search to use generic semantic:read scope

This implements ADR-009, which documents the decision to use a generic
`semantic:read` OAuth scope instead of requiring all app-specific scopes
for semantic search functionality.

Changes:
- Created new `nextcloud_mcp_server/models/semantic.py` with semantic search models
  - SemanticSearchResult (with new doc_type field for multi-app support)
  - SemanticSearchResponse
  - SamplingSearchResponse
  - VectorSyncStatusResponse

- Created new `nextcloud_mcp_server/server/semantic.py` with semantic search tools
  - nc_semantic_search (renamed from nc_notes_semantic_search)
  - nc_semantic_search_answer (renamed from nc_notes_semantic_search_answer)
  - nc_get_vector_sync_status (renamed from nc_notes_get_vector_sync_status)
  - All tools now use @require_scopes("semantic:read") instead of "notes:read"

- Updated `nextcloud_mcp_server/server/notes.py`
  - Removed semantic search tools (moved to semantic.py)
  - Removed semantic search model imports
  - Removed unused MCP imports (ModelHint, ModelPreferences, etc.)

- Updated `nextcloud_mcp_server/models/notes.py`
  - Removed semantic search models (moved to semantic.py)

- Updated `nextcloud_mcp_server/app.py`
  - Import configure_semantic_tools
  - Register semantic tools when VECTOR_SYNC_ENABLED=true

- Updated `nextcloud_mcp_server/server/__init__.py`
  - Export configure_semantic_tools

- Updated tests
  - tests/integration/test_sampling.py: Use new tool names
  - tests/unit/test_response_models.py: Import from semantic.py, add doc_type field

Architecture:
- Semantic search is now a cross-app feature, not tied to Notes
- Uses dual-phase authorization: semantic:read scope + per-document verification
- Supports future multi-app indexing (notes, calendar, deck, files, contacts)

Test results:
- All 69 unit tests passing
- All 5 smoke tests passing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

nextcloud_mcp_server/app.py

@@ -45,6 +45,7 @@ from nextcloud_mcp_server.server import (
     configure_cookbook_tools,
     configure_deck_tools,
     configure_notes_tools,
+    configure_semantic_tools,
     configure_sharing_tools,
     configure_tables_tools,
     configure_webdav_tools,
@@ -871,6 +872,14 @@ def get_app(transport: str = "sse", enabled_apps: list[str] | None = None):
                 f"Unknown app: {app_name}. Available apps: {list(available_apps.keys())}"
             )
 
+    # Register semantic search tools (cross-app feature)
+    settings = get_settings()
+    if settings.vector_sync_enabled:
+        logger.info("Configuring semantic search tools (vector sync enabled)")
+        configure_semantic_tools(mcp)
+    else:
+        logger.info("Skipping semantic search tools (VECTOR_SYNC_ENABLED not set)")
+
     # Register OAuth provisioning tools (only when offline access is enabled)
     # With token exchange enabled (external IdP), provisioning is not needed for MCP operations
     enable_token_exchange = (