fix(jobbank-search)!: emit deadline as YYYY-MM-DD in search output

The feed's DD.MM.YYYY parenthetical passed through raw - documented, but
contradicting the /scrape contract, every other portal, and this CLI's
own detail command for the same job, and ambiguous to a date parser
(01.09.2026: 1 Sep or 9 Jan). The known shape converts to ISO; løbende
still maps to null; unrecognized shapes pass through for /rank's
defensive handling. Breaking for anything parsing the old format - the
README's own search example already showed ISO. Review finding F5
(2026-08-19), decision approved by Mads.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.agents/skills/jobbank-search/cli/tests/search-normalization.test.ts

@@ -33,6 +33,6 @@ describe("Jobbank search normalization", () => {
     expect(result.company).toBe("Acme A/S");
     expect(result.location).toBe("København");
     expect(result.url).toBe("https://jobbank.dk/job/12345/acme/data-scientist");
-    expect(result.deadline).toBe("31.07.2026");
+    expect(result.deadline).toBe("2026-07-31");
   });
 });