feat(chunking): add AST-aware code chunking for Go, Python, TypeScript

- [x] Add language-specific chunkers with AST parsing (Go, Python, TypeScript)
- [x] Implement chunking manager to dispatch files to appropriate chunkers
- [x] Integrate code chunks into vector sync for semantic search
- [x] Add tree-sitter dependency for Python/TypeScript parsing
- [x] Reorder struct fields for consistency across codebase
- [x] Rename error variables to follow Go conventions (err → unmarshalErr, etc.)
- [x] Add code chunk metadata to vector documents (language, symbol name, line ranges)
- [x] Update worker service to initialize chunking pipeline with all three languages

internal/vector/sqlitevec/helpers.go

@@ -8,21 +8,22 @@ const (
 	DocTypeObservation    DocType = "observation"
 	DocTypeSessionSummary DocType = "session_summary"
 	DocTypeUserPrompt     DocType = "user_prompt"
+	DocTypeCodeChunk      DocType = "code_chunk"
 )
 
 // Document represents a document to store with vector embedding.
 type Document struct {
+	Metadata map[string]any
 	ID       string
 	Content  string
-	Metadata map[string]any
 }
 
 // QueryResult represents a search result from vector search.
 type QueryResult struct {
+	Metadata   map[string]any
 	ID         string
 	Distance   float64
-	Similarity float64 // 1.0 = identical, 0.0 = opposite (derived from distance)
-	Metadata   map[string]any
+	Similarity float64
 }
 
 // DistanceToSimilarity converts sqlite-vec cosine distance to similarity score.