feat(leann-phase2): implement hybrid vector storage and graph-based search

- [x] Add AST-aware code chunking for Go, Python, and TypeScript using tree-sitter
- [x] Implement LEANN-inspired hybrid vector storage with hub detection and selective embedding storage (60-80% savings)
- [x] Add observation relationship graph with CSR format and edge detection (file overlap, semantic similarity, temporal, concept)
- [x] Implement graph-aware search with two-level traversal and relationship-based ranking
- [x] Add auto-tuning system for dynamic hub threshold adjustment based on query performance
- [x] Add comprehensive metrics tracking for vector storage, queries, latency, and graph traversals
- [x] Update configuration system with graph and hybrid storage settings
- [x] Add graph stats and vector metrics endpoints to worker service
- [x] Enhance UI sidebar with advanced metrics display and graph visualization
- [x] Optimize struct field alignment throughout codebase for memory efficiency
- [x] Update documentation with LEANN Phase 2 features and performance benefits
- [x] Add tree-sitter dependency for AST parsing

pkg/models/relation.go

@@ -60,14 +60,14 @@ const (
 
 // ObservationRelation represents a directed relationship between two observations.
 type ObservationRelation struct {
-	ID              int64                   `db:"id" json:"id"`
-	SourceID        int64                   `db:"source_id" json:"source_id"`
-	TargetID        int64                   `db:"target_id" json:"target_id"`
 	RelationType    RelationType            `db:"relation_type" json:"relation_type"`
-	Confidence      float64                 `db:"confidence" json:"confidence"`
 	DetectionSource RelationDetectionSource `db:"detection_source" json:"detection_source"`
 	Reason          string                  `db:"reason" json:"reason,omitempty"`
 	CreatedAt       string                  `db:"created_at" json:"created_at"`
+	ID              int64                   `db:"id" json:"id"`
+	SourceID        int64                   `db:"source_id" json:"source_id"`
+	TargetID        int64                   `db:"target_id" json:"target_id"`
+	Confidence      float64                 `db:"confidence" json:"confidence"`
 	CreatedAtEpoch  int64                   `db:"created_at_epoch" json:"created_at_epoch"`
 }
 
@@ -88,12 +88,12 @@ func NewObservationRelation(sourceID, targetID int64, relType RelationType, conf
 
 // RelationDetectionResult contains the result of relation detection.
 type RelationDetectionResult struct {
-	SourceID        int64
-	TargetID        int64
 	RelationType    RelationType
-	Confidence      float64
 	DetectionSource RelationDetectionSource
 	Reason          string
+	SourceID        int64
+	TargetID        int64
+	Confidence      float64
 }
 
 // DetectFileOverlapRelation checks if observations share file references and determines relationship type.
@@ -484,6 +484,6 @@ type RelationWithDetails struct {
 
 // RelationGraph represents a graph of related observations.
 type RelationGraph struct {
-	CenterID  int64                  `json:"center_id"`
 	Relations []*RelationWithDetails `json:"relations"`
+	CenterID  int64                  `json:"center_id"`
 }