Enable Wellfound apply: fix missing apply_type, add submit verification

- Search now sets apply_type: 'wellfound' on discovered jobs (was missing,
  so applier silently skipped all Wellfound jobs)
- Add Wellfound to DEFAULT_ENABLED_APPLY_TYPES (LinkedIn first, then Wellfound)
- Sort platform processing order: linkedin → wellfound → external
- Apply handler: add closed listing detection, submit verification,
  error handling on meta extraction

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

lib/wellfound.mjs

@@ -69,6 +69,7 @@ export async function searchWellfound(page, search, { onPage } = {}) {
           results.push({
             id: `wf_${slug}`,
             platform: 'wellfound',
+            apply_type: 'wellfound',
             track,
             title,
             company,