feat: Vestige v2.0.0 "Cognitive Leap" — 3D dashboard, HyDE search, WebSocket events

The biggest release in Vestige history. Complete visual and cognitive overhaul.

Dashboard:
- SvelteKit 2 + Three.js 3D neural visualization at localhost:3927/dashboard
- 7 interactive pages: Graph, Memories, Timeline, Feed, Explore, Intentions, Stats
- WebSocket event bus with 16 event types, real-time 3D animations
- Bloom post-processing, GPU instanced rendering, force-directed layout
- Dream visualization mode, FSRS retention curves, command palette (Cmd+K)
- Keyboard shortcuts, responsive mobile layout, PWA installable
- Single binary deployment via include_dir! (22MB)

Engine:
- HyDE query expansion (intent classification + 3-5 semantic variants + centroid)
- fastembed 5.11 with optional Nomic v2 MoE + Qwen3 reranker + Metal GPU
- Emotional memory module (#29)
- Criterion benchmark suite

Backend:
- Axum WebSocket at /ws with heartbeat + event broadcast
- 7 new REST endpoints for cognitive operations
- Event emission from MCP tools via shared broadcast channel
- CORS for SvelteKit dev mode

Distribution:
- GitHub issue templates (bug report, feature request)
- CHANGELOG with comprehensive v2.0 release notes
- README updated with dashboard docs, architecture diagram, comparison table

734 tests passing, zero warnings, 22MB release binary.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/vestige-core/src/memory/node.rs

@@ -148,6 +148,30 @@ pub struct KnowledgeNode {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub valid_until: Option<DateTime<Utc>>,
 
+    // ========== Utility Tracking (MemRL v1.9.0) ==========
+    /// Utility score = times_useful / times_retrieved (0.0 to 1.0)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub utility_score: Option<f64>,
+    /// Number of times this memory was retrieved in search
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub times_retrieved: Option<i32>,
+    /// Number of times this memory was subsequently useful
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub times_useful: Option<i32>,
+
+    // ========== Emotional Memory (v2.0.0) ==========
+    /// Emotional valence: -1.0 (negative) to 1.0 (positive)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub emotional_valence: Option<f64>,
+    /// Flashbulb memory flag: ultra-high-fidelity encoding
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub flashbulb: Option<bool>,
+
+    // ========== Temporal Hierarchy (v2.0.0) ==========
+    /// Temporal level for summary nodes: None=leaf, "daily"/"weekly"/"monthly"
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub temporal_level: Option<String>,
+
     // ========== Semantic Embedding ==========
     /// Whether this node has an embedding vector
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -181,6 +205,12 @@ impl Default for KnowledgeNode {
             tags: vec![],
             valid_from: None,
             valid_until: None,
+            utility_score: None,
+            times_retrieved: None,
+            times_useful: None,
+            emotional_valence: None,
+            flashbulb: None,
+            temporal_level: None,
             has_embedding: None,
             embedding_model: None,
         }