refactor: low-regret cleanup across core, engine, dashboard

- core: extract ai-engine-loader.ts to share @fusion/engine dynamic-import
  boilerplate between ai-summarize and memory-compaction (incl. AgentMessage
  type); collapse getInbox/getOutbox, listInsights/countInsights,
  listRuns/countRuns, and three hasProjectDb* variants behind shared helpers.
- core: drop unused pluginLoaderLog export; tighten two `any` casts
  (db.walCheckpoint row, plugin-loader error.code).
- engine: extract resolveRoleFallback helper from buildSessionSkillContext/Sync;
  remove 22 stale `eslint-disable no-explicit-any` directives across
  project-engine, self-healing, triage, worktree-pool.
- dashboard: apply ESLint autofix (let→const, empty `interface extends`→type).

All three packages: typecheck clean, full test suites pass (14,414 tests),
builds clean. Net lint: -31 warnings. No public behavior changes.

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

packages/core/src/db.ts

@@ -1672,7 +1672,9 @@ export class Database {
    * Safe to call periodically. Returns checkpoint stats.
    */
   walCheckpoint(): { busy: number; log: number; checkpointed: number } {
-    const row = this.db.prepare("PRAGMA wal_checkpoint(TRUNCATE)").get() as any;
+    const row = this.db.prepare("PRAGMA wal_checkpoint(TRUNCATE)").get() as
+      | { busy?: number; log?: number; checkpointed?: number }
+      | undefined;
     return { busy: row?.busy ?? 0, log: row?.log ?? 0, checkpointed: row?.checkpointed ?? 0 };
   }