feat: revive datacareer.ch and integrate basel-jobs.ch

datacareer.ch had been returning 403 on every page for months. The cause
was our own User-Agent: its nginx inverts the usual bot rule and blocks
browser-like UAs while serving honest ones (no UA, curl, Googlebot).
Give it PLAIN_HEADERS instead of the shared spoofed-Chrome HEADERS.
Basel has 8 jobs on a single page with no pagination, so page 2 returning
0 items is correct rather than truncation.

basel-jobs.ch was documented as un-integrable because DataDome blocks
plain curl. Only half of that was true. Measured: plain fetch 403s on any
UA, headless Chrome over CDP 403s, Playwright's own launch 403s even
headful — but a real Chrome launched normally with --remote-debugging-port
and attached over CDP afterwards gets 200. Clearance then lives entirely
in a datadome cookie that replays fine over plain fetch with a matching
UA, so a browser is touched only to mint, never to scrape. The earlier
"cookie can't be extracted" note was true of the browser extension, not
of CDP.

Minting needs a visible window, so launchd runs can't do it; a stale
cookie makes the source log and yield nothing instead of failing the run.
Refresh by hand with `bun run mint-datadome`, or set LINKME_NO_BROWSER=1.

Three passes, all needed — they cover different sets. The informatik
category is a curated taxonomy, not the whole board, and the two search
modes query different indexes: websearch=1 finds role words and postings
filed outside IT (+147 over the category), while the bare search is the
only mode matching stack terms — react, frontend and backend return zero
under websearch=1. Language checks run against div.plain-content only;
against the whole page the German site chrome alone clears the DE/FR
threshold and drops every job, English ones included.

Also fix a pre-existing double-wrapped Promise in the extraSources type.

scripts/mint-datadome.ts

@@ -0,0 +1,15 @@
+/**
+ * Refresh the basel-jobs.ch DataDome cookie.
+ *
+ * Opens a real Chrome window for a few seconds — headless and Playwright-launched
+ * browsers are both fingerprinted and blocked, so this cannot run unattended.
+ * Run it by hand when `bun fetch` reports basel-jobs.ch as unavailable.
+ */
+import { mintDataDomeSession } from "../fetch-other.ts";
+
+const session = await mintDataDomeSession();
+if (!session) {
+  console.error("failed to mint a DataDome cookie");
+  process.exit(1);
+}
+console.log(`ok — minted ${session.mintedAt}`);