Stop the strict acceptance from waiting for itself

A scenario whose body ran past about 19 s idled until 45 s after its
start, and twice one never exited and hit the runner's 300 s timeout
after it had passed: something of Chrome outlived Browser.close and kept
its stdout and stderr open.

- scripts/qa/browser.mjs closes Chrome within 5 s, kills its process
  group and closes its pipes; the harness then finishes and exits with
  the scenario's code. QA_EXIT_DIAGNOSTICS=1 keeps the old ending and
  prints the open handles and Chrome's process tree 5 s after finish.
- Every strict page starts with its clock at the 18:30 UTC nearest to
  the real time, so Navara's sun is up over the test cities whenever the
  acceptance runs; a scenario can ask for its own instant or the real
  clock (Wildlife does, for its freshness fixtures).
- The runner records a scenario that passed but did not exit as hung,
  kills the whole process group on a timeout, runs a failed scenario
  once more and reports one that passes then as flaky, and appends each
  run to --history=FILE; scripts/report-acceptance-flake.mjs reads it.

scripts/qa-imagery-contract.mjs

@@ -6,6 +6,7 @@
 //
 //   node scripts/qa-imagery-contract.mjs http://127.0.0.1:<PORT>
 //     [--layers=recent-imagery] [--evidence=FILE]
+import { closeBrowser } from './qa/browser.mjs';
 import fs from 'node:fs/promises';
 import os from 'node:os';
 import path from 'node:path';
@@ -470,9 +471,8 @@ try {
   report.errors.push(e.stack);
   check('driver completes', false);
 } finally {
-  await browser.close();
+  await closeBrowser(browser);
   await fs.writeFile(output, JSON.stringify(report, null, 2));
 }
 const failed = report.checks.some((c) => !c.pass);
-await strict.finish({ failed: failed ? 'imagery checks failed' : null });
-if (failed) process.exitCode = 1;
+await strict.finishAndExit({ failed: failed ? 'imagery checks failed' : null });