feat: implement semantic search tool and fix vector sync issues (ADR-007 Phase 3)

Completes the ADR-007 implementation by adding user-facing semantic search
functionality. Previous phases implemented scanner and processor for background
indexing; this adds the query interface.

Changes:
- Add nc_notes_semantic_search MCP tool for natural language queries
- Fix Qdrant point IDs to use UUIDs instead of strings (was causing 400 errors)
- Reduce scan interval default from 1 hour to 5 minutes for faster updates
- Add SemanticSearchResult and SemanticSearchNotesResponse models
- Implement dual-phase authorization (Qdrant filter + Nextcloud API verification)

The semantic search enables finding notes by meaning rather than exact keywords,
using vector embeddings to understand query intent. Point ID fix resolves
critical bug where all document indexing failed with "invalid point ID" errors.

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

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

nextcloud_mcp_server/models/notes.py

@@ -37,6 +37,18 @@ class NoteSearchResult(BaseModel):
     score: Optional[float] = Field(None, description="Search relevance score")
 
 
+class SemanticSearchResult(BaseModel):
+    """Model for semantic search results with additional metadata."""
+
+    id: int = Field(description="Note ID")
+    title: str = Field(description="Note title")
+    category: str = Field(default="", description="Note category")
+    excerpt: str = Field(description="Excerpt from matching chunk")
+    score: float = Field(description="Semantic similarity score (0-1)")
+    chunk_index: int = Field(description="Index of matching chunk in document")
+    total_chunks: int = Field(description="Total number of chunks in document")
+
+
 class NotesSettings(BaseModel):
     """Model for Notes app settings."""
 
@@ -83,3 +95,16 @@ class SearchNotesResponse(BaseResponse):
     results: List[NoteSearchResult] = Field(description="Search results")
     query: str = Field(description="The search query used")
     total_found: int = Field(description="Total number of notes found")
+
+
+class SemanticSearchNotesResponse(BaseResponse):
+    """Response model for semantic search."""
+
+    results: List[SemanticSearchResult] = Field(
+        description="Semantic search results with similarity scores"
+    )
+    query: str = Field(description="The search query used")
+    total_found: int = Field(description="Total number of notes found")
+    search_method: str = Field(
+        default="semantic", description="Search method used (semantic or hybrid)"
+    )