fix(clippy): Rust 1.95 compatibility — sort_by_key + collapsible_match

CI runs on stable Rust which advanced from 1.93 to 1.95, introducing
two newly-enforced lints under -D warnings:

- clippy::unnecessary_sort_by (12 sites) — rewrite sort_by closures
  that only call .cmp on Copy keys as sort_by_key, using std::cmp::Reverse
  for the descending ones.
- clippy::collapsible_match (1 site) — merge the MemoryState::Dormant
  inner if into a match guard. The equivalent rewrite for the Ping/Pong
  arm in websocket.rs is blocked by a move of non-Copy Bytes across the
  match-guard boundary, so that one site gets an explicit #[allow].

Files touched:
- crates/vestige-core/src/advanced/{chains,compression,cross_project,reconsolidation}.rs
- crates/vestige-core/src/codebase/{git,relationships}.rs
- crates/vestige-core/src/neuroscience/{importance_signals,memory_states,predictive_retrieval}.rs
- crates/vestige-mcp/src/tools/{changelog,cross_reference}.rs
- crates/vestige-mcp/src/dashboard/websocket.rs

Verified: cargo clippy --workspace -- -D warnings green on rustc 1.95.0;
cargo test --workspace unchanged (1292 tests green).

crates/vestige-mcp/src/dashboard/websocket.rs

@@ -123,6 +123,9 @@ async fn handle_socket(socket: WebSocket, state: AppState) {
             msg = receiver.next() => {
                 match msg {
                     Some(Ok(Message::Close(_))) | None => break,
+                    // Match guards can't move out of the bound `data` (Bytes is
+                    // not Copy), so the nested `if` is required here.
+                    #[allow(clippy::collapsible_match, clippy::collapsible_if)]
                     Some(Ok(Message::Ping(data))) => {
                         if sender.send(Message::Pong(data)).await.is_err() {
                             break;

crates/vestige-mcp/src/tools/changelog.rs

@@ -237,7 +237,7 @@ fn execute_system_wide(
     }
 
     // Sort by timestamp descending
-    events.sort_by(|a, b| b.0.cmp(&a.0));
+    events.sort_by_key(|b| std::cmp::Reverse(b.0));
 
     // Truncate to limit
     events.truncate(limit as usize);

crates/vestige-mcp/src/tools/cross_reference.rs

@@ -560,7 +560,7 @@ pub async fn execute(
 
     // Sort by date descending for supersession
     let mut by_date = scored.iter().collect::<Vec<_>>();
-    by_date.sort_by(|a, b| b.updated_at.cmp(&a.updated_at));
+    by_date.sort_by_key(|b| std::cmp::Reverse(b.updated_at));
 
     for i in 0..by_date.len() {
         for j in (i + 1)..by_date.len() {