fix(portal-clis): emit the contract's id field from jobnet and jobdanmark search results (#518)

/add-portal's contract says every search result carries at least id,
title, company, location, date, url, and the four other shipped CLIs
emit id. When #340 added the company/location/date/url aliases to these
two, id was left out: jobnet exposed the value only as jobAdId,
jobdanmark only as slug, so a consumer reading every portal's JSON
through one shape had to special-case both to call detail.

Purely additive: id equals jobAdId on jobnet and slug on jobdanmark, the
native keys stay, nothing is renamed. Each SKILL.md notes the alias. The
additive-contract test in each CLI now asserts id and its equality with
the native key; both fail on master.

.agents/skills/jobnet-search/SKILL.md

@@ -69,7 +69,7 @@ Key flags:
 bun run .agents/skills/jobnet-search/cli/src/cli.ts detail <jobAdId> [--format json|plain]
 ```
 
-`jobAdId` is the UUID from `search` results (the `jobAdId` field). Returns the complete job
+`jobAdId` is the UUID from `search` results (the `jobAdId` field, also emitted as `id`, the portal-contract name every search CLI shares). Returns the complete job
 description, contact persons, application deadline, employer details, and direct application URL.
 
 ### Search occupation types