refactor: extract magic numbers to constants, fix audit issues

- Centralize all magic numbers/strings in lib/constants.mjs
- Fix double-replaced import names in filter.mjs
- Consolidate duplicate fs imports in job_applier/job_searcher
- Remove empty JSDoc block in job_searcher
- Update keywords.mjs model from claude-3-haiku to claude-haiku-4-5
- Extract Anthropic API URLs to constants
- Convert :has-text() selectors to page.locator() API
- Fix SIGTERM handler conflict — move partial-run notification into lock.onShutdown
- Remove unused exports (LOCAL_USER_AGENT, DEFAULT_REVIEW_WINDOW_MINUTES)
- Fix variable shadowing (b -> v) in job_filter reduce callback
- Replace SKILL.md PM2 references with system cron

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

job_searcher.mjs

@@ -6,8 +6,7 @@
  */
 import { loadEnv } from './lib/env.mjs';
 loadEnv(); // load .env before anything else
-/**
- */
+
 import { dirname, resolve } from 'path';
 import { fileURLToPath } from 'url';
 
@@ -35,15 +34,6 @@ async function main() {
 
   const settings = loadConfig(resolve(__dir, 'config/settings.json'));
 
-  // Send notification even if SIGTERM kills the process mid-run
-  process.once('SIGTERM', async () => {
-    if (totalAdded > 0) {
-      const summary = formatSearchSummary(totalAdded, totalSeen - totalAdded, platformsRun.length ? platformsRun : ['LinkedIn']);
-      await sendTelegram(settings, summary + '\n_(partial run — timed out)_').catch(() => {});
-    }
-    process.exit(0);
-  });
-
   const writeLastRun = (finished = false) => {
     const entry = {
       started_at: startedAt,
@@ -68,9 +58,13 @@ async function main() {
     writeFileSync(runsPath, JSON.stringify(runs, null, 2));
   };
 
-  lock.onShutdown(() => {
+  lock.onShutdown(async () => {
     console.log('  Writing partial results to last-run file...');
     writeLastRun(false);
+    if (totalAdded > 0) {
+      const summary = formatSearchSummary(totalAdded, totalSeen - totalAdded, platformsRun.length ? platformsRun : ['LinkedIn']);
+      await sendTelegram(settings, summary + '\n_(partial run — interrupted)_').catch(() => {});
+    }
   });
 
   // Load config