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>

lib/keywords.mjs

@@ -3,6 +3,8 @@
  * One Claude call per search track using full profile + search config context
  */
 
+import { ANTHROPIC_API_URL } from './constants.mjs';
+
 export async function generateKeywords(search, profile, apiKey) {
   if (!apiKey) throw new Error('ANTHROPIC_API_KEY not set');
 
@@ -38,7 +40,7 @@ Think about:
 Return ONLY a JSON array of strings, no explanation, no markdown.
 Example format: ["query one", "query two", "query three"]`;
 
-  const res = await fetch('https://api.anthropic.com/v1/messages', {
+  const res = await fetch(ANTHROPIC_API_URL, {
     method: 'POST',
     headers: {
       'Content-Type': 'application/json',
@@ -46,7 +48,7 @@ Example format: ["query one", "query two", "query three"]`;
       'anthropic-version': '2023-06-01'
     },
     body: JSON.stringify({
-      model: 'claude-3-haiku-20240307',
+      model: 'claude-haiku-4-5-20251001',
       max_tokens: 1024,
       messages: [{ role: 'user', content: prompt }]
     })