chore: clean up dead code, use shared loadConfig, cache queue I/O

- Remove unused readFileSync import from job_applier.mjs
- Remove unused makeJobId (dead code, nothing imports it)
- setup.mjs: use shared loadConfig instead of inline cfg()
- queue.mjs: add in-memory cache for queue and log to avoid
  redundant disk reads during a single run

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

job_applier.mjs

@@ -4,7 +4,7 @@
  * Reads jobs queue and applies to each new/needs_answer job
  * Run via cron or manually: node job_applier.mjs [--preview]
  */
-import { readFileSync, existsSync } from 'fs';
+import { existsSync } from 'fs';
 import { dirname, resolve } from 'path';
 import { fileURLToPath } from 'url';