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-mcp/src/tools/search_unified.rs

@@ -299,6 +299,19 @@ pub async fn execute(
         }
     }
 
+    // ====================================================================
+    // STAGE 5C: Utility-based ranking (MemRL-inspired)
+    // Memories that proved useful in past sessions get a retrieval boost.
+    // utility_score = times_useful / times_retrieved (0.0 to 1.0)
+    // ====================================================================
+    for result in &mut filtered_results {
+        let utility = result.node.utility_score.unwrap_or(0.0) as f32;
+        if utility > 0.0 {
+            // Utility boost: up to +15% for memories with utility_score = 1.0
+            result.combined_score *= 1.0 + (utility * 0.15);
+        }
+    }
+
     // Re-sort by adjusted combined_score (descending) after all score modifications
     filtered_results.sort_by(|a, b| {
         b.combined_score