perf(dashboard): index tasks.column/updatedAt and debounce detail fetches

Speeds up task-list load and interaction for projects with 100+ tasks.

- Migration 59 adds idxTasksColumn and idxTasksUpdatedAt; listTasks()
  filters by "column" on every board load and SSE/refresh paths sort by
  updatedAt, so each query was previously a full table scan plus a temp
  B-tree sort.
- Debounce handleEmbeddedOpenDetail in ListView so rapid keyboard/mouse
  navigation no longer fires a heavy /tasks/:id (log + comments) per
  selection; stale-target requests short-circuit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/src/db.ts

@@ -88,7 +88,7 @@ export function probeFts5(db: DatabaseSync): boolean {
 
 // ── Schema Definition ────────────────────────────────────────────────
 
-const SCHEMA_VERSION = 58;
+const SCHEMA_VERSION = 59;
 
 function normalizeTaskComments(
   steeringComments: SteeringComment[] | undefined,
@@ -2246,6 +2246,17 @@ export class Database {
       });
     }
 
+    // Dashboard load performance for projects with 100+ tasks.
+    // listTasks() filters by "column" and the SSE/refresh paths sort by
+    // updatedAt; neither column had an index, so each board load did a
+    // full table scan + temp B-tree sort.
+    if (version < 59) {
+      this.applyMigration(59, () => {
+        this.db.exec(`CREATE INDEX IF NOT EXISTS idxTasksColumn ON tasks("column")`);
+        this.db.exec(`CREATE INDEX IF NOT EXISTS idxTasksUpdatedAt ON tasks(updatedAt DESC)`);
+      });
+    }
+
   }
 
   /**