test(search): make /api/search e2e tests self-contained (fix red develop after #52)

[joewiz]

[This PR was co-authored with Claude Code. -Joe]

Summary

Fix the failing search.cy.js e2e tests that turned develop red after #52, by making them self-contained instead of dependent on the built-in doc app.

Why develop went red

#52 moved /api/search to query the shared site-content Lucene field. But search.cy.js assumed the built-in doc app would be findable (?q=xquery, &app=doc), and the doc app does not populate site-content — so on a bare existdb-openapi install (the CI image) the search returns nothing. Three assertions failed:

1) returns the documented shape …    AssertionError: expected 0 to be above 0
2) wraps matched terms in <mark> …   expected undefined to exist
3) exposes a canonical identifier …  Target cannot be null or undefined

(1) is the root cause — total was 0; (2) and (3) cascade off the empty result set.

Fix

Seed a self-contained fixture rather than relying on the image's content:

• A before() hook stores a small collection at /db/apps/cypress-search-test with a site-content index — 6 <page> docs containing "xquery" across two sections — and reindexes, via admin XQuery through /api/query. after() removes it.
• The suite searches its own corpus, exercising the real shared-field contract: relevance ordering, <mark> highlighting, per-document dedup, offset/limit paging, and the app facet.

This also removes an accidental coupling: the tests had been passing only because the image happened to ship the doc app; several content assertions were in fact passing vacuously on an empty result set once the field changed.

Verification

Run end-to-end on a live existdb-openapi instance: the setup runs via /api/query, ?q=xquery returns the 6 fixture docs with <mark> snippets and highlights[], and ?app=cypress-search-test restricts to the fixture. The other 10 specs (db, query, packages, parity, site, system, users, langservice, query_scope, query_pool_reuse) are unaffected.

Note

Surfaced because #52 was merged with this CI already red. This PR is the fix-forward; with it, develop's Cypress run goes green again.