fix: security/bug fixes, extract constants, remove magic values

- Remove random suffix from Wellfound job IDs (broke dedup)
- Add null coalescing to all profile field returns in form_filler
- Fix honeypot case referencing nonexistent results.skipped counter
- Remove unused makeJobId import from linkedin.mjs
- Navigate directly to job URL instead of search+click in linkedin apply
- Add Telegram notification rate limiting (1.5s between sends)
- Replace Mode B blocking sleep with --preview flag
- Add max_applications_per_run enforcement
- Remove tracked search_config.json (keep .example.json only)
- Add search_config.json to .gitignore, fix duplicate node_modules entry
- Extract all magic numbers/strings to lib/constants.mjs

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

config/search_config.json

@@ -1,41 +0,0 @@
-{
-  "_note": "Configure your job searches here. Each search runs on both listed platforms.",
-  "first_run_days": 90,
-  "searches": [
-    {
-      "name": "Founding GTM",
-      "track": "gtm",
-      "keywords": [
-        "founding account executive",
-        "first sales hire",
-        "first GTM hire",
-        "founding AE",
-        "head of sales startup remote"
-      ],
-      "platforms": ["linkedin", "wellfound"],
-      "filters": {
-        "remote": true,
-        "posted_within_days": 2
-      },
-      "exclude_keywords": ["BDR", "SDR", "staffing", "insurance", "retail", "consumer", "recruiter", "DataAnnotation"],
-      "salary_min": 130000
-    },
-    {
-      "name": "Enterprise AE",
-      "track": "ae",
-      "keywords": [
-        "enterprise account executive SaaS remote",
-        "senior account executive technical SaaS remote",
-        "enterprise AE data infrastructure cloud"
-      ],
-      "platforms": ["linkedin"],
-      "filters": {
-        "remote": true,
-        "posted_within_days": 2,
-        "easy_apply_only": true
-      },
-      "exclude_keywords": ["BDR", "SDR", "SMB", "staffing", "retail", "DataAnnotation"],
-      "salary_min": 150000
-    }
-  ]
-}