refactor: normalize apply statuses, remove dead code, fix signal handler

- lib/apply/index.mjs: add STATUS_MAP to normalize platform-specific statuses
  to generic ones (no_button/no_submit/no_modal → skipped_no_apply).
  Documented all generic statuses for AI/developer reference.
- job_applier.mjs: handleResult now handles skipped_no_apply, default case
  logs + saves instead of silently dropping
- lib/linkedin.mjs: remove dead applyLinkedIn() and detectAts(), clean imports
  (~110 lines removed). Search-only module now.
- lib/wellfound.mjs: remove dead applyWellfound(), clean imports.
  Search-only module now.
- lib/lock.mjs: fix async signal handler — shutdown handlers now actually
  complete before process.exit()
- test_linkedin_login.mjs: add try/catch/finally with proper browser cleanup
- README: update status table with all current statuses

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

lib/lock.mjs

@@ -29,18 +29,21 @@ export function acquireLock(name, dataDir) {
 
   // Graceful shutdown — call registered cleanup before exiting
   const shutdownHandlers = [];
-  const shutdown = (code) => async () => {
+  const shutdown = (code) => {
     console.log(`\n⚠️  ${name}: signal received, shutting down gracefully...`);
-    for (const fn of shutdownHandlers) {
-      try { await fn(); } catch {}
-    }
-    release();
-    process.exit(code);
+    // Run handlers sequentially, then exit
+    (async () => {
+      for (const fn of shutdownHandlers) {
+        try { await fn(); } catch {}
+      }
+      release();
+      process.exit(code);
+    })();
   };
 
   process.on('exit', release);
-  process.on('SIGINT', shutdown(130));
-  process.on('SIGTERM', shutdown(143));
+  process.on('SIGINT', () => shutdown(130));
+  process.on('SIGTERM', () => shutdown(143));
 
   return { release, onShutdown: (fn) => shutdownHandlers.push(fn) };
 }