fix(theme): keep facet selections in the URL

[marevol]

Why

With the bootstrap static theme as the default search UI, facet selections (the label facet and the facet query views such as date, size and file type) were kept only in memory; search.js said so explicitly ("facet selections stay in memory"). After narrowing a search with a facet, the address bar still showed the unfiltered search, so a reload, a link sent to a colleague, or Back from a result document dropped the filter and showed unfiltered results. The JSP search pages put the selections in the URL as ex_q.

What changes

• search.js:
  • syncStartParam() becomes syncUrlParams() and writes the facet selections as ex_q clauses besides start=, in place (replaceState), as the page offset already was. A facet click still does not add a history entry.
  • runFromUrl() sorts the URL's ex_q clauses back into the stores the facet groups read: label:<value> into the label facet, values of the configured facet query views into those views, and anything else (e.g. from advanced search) into the pass-through list as before. A repeated clause is sent once. Restored selections render active, and a click removes them from the request and the URL.
  • The request is built from the same list (exQClauses()), so the URL and the request cannot drift apart.
• search.test.js: tests for writing, restoring, deselecting and de-duplicating; the existing test for a facet click resetting start= now expects the ex_q it adds.

The theme version stays 1.3.0: it was set for 15.9 and has not been released yet.

Verification

• Theme JS tests (src/test/js, npx vitest run): 577 passed. The five new or changed cases fail on main.
• mvn test -Dtest=BundledBootstrapThemeTest: 125 tests passed.
• Headless Chromium against a distribution built with this change, OpenSearch 3.8, 12 documents of which 4 carry the label "Team Docs"; search, click the label facet, reload. Before (main) → after:

Step	Before	After
After the facet click	URL /search?q=facetword, 4 hits	URL /search?q=facetword&ex_q=label%3Ateamdocs, 4 hits
After reload	10 hits (of 12), no active facet, request without ex_q	4 hits, "Team Docs" active, request with ex_q=label:teamdocs