fix(job-key): fold Latin letters without an NFKD decomposition and add --audit --migrate (#637)

* fix(job-key): fold Latin letters without an NFKD decomposition and add --audit --migrate

Closes #537

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* refactor(job-key): drop the redundant NFC before NFKD

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* fix(job-key): extend the fold to ı ħ ĸ ŋ ŧ, ignore migrate backups, correct NFC wording

Fold the remaining Latin Extended-A letters without an NFKD decomposition
(ı→i, ħ/Ħ→h, ĸ→k, ŋ/Ŋ→ng, ŧ/Ŧ→t, per Unidecode 1.4.0), so "Kılıç" keys
as "kilic" instead of "klc". Gitignore the seen_jobs.json.bak-* backups
written by --audit --migrate and require the rule in security_guards.
The CHANGELOG and a test comment still described an NFC pass; the fold
runs after NFKD and there is no NFC.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* chore: drop the CHANGELOG hunk, frozen by #800 (release notes come from the PR title)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>
Co-authored-by: Mads Lorentzen <madslorentzen_17@hotmail.com>

.gitignore

@@ -25,6 +25,8 @@ salary_data.json
 # its own directory, so these land at .claude/skills/job-scraper/job_scraper/*.
 # A rooted `job_scraper/...` pattern silently fails to match them.
 **/job_scraper/seen_jobs.json
+# Backups written by `tools/job_key.py --audit --migrate` hold the same history.
+**/job_scraper/seen_jobs.json.bak-*
 **/job_scraper/notion_sync.json
 **/job_scraper/*.md
 *_BehavioralReport.pdf