test(search): add SearchAPIImpl phase-routing and permission-filtering integration tests

[fabrizzio-dotCMS]

Context

PR #35609 introduced SearchAPIImpl (the phase-aware router) and OSSearchAPIImpl. The existing OSSearchAPIImplIntegrationTest tests the OS implementation directly against empty indices. The following coverage gaps were identified in the PR review and deferred to this issue.

Missing test coverage

1. Phase routing selects the correct provider

• Phase 0 / 1 → ESSearchAPIImpl is used
• Phase 2 / 3 → OSSearchAPIImpl is used
• Requires injecting SearchAPIImpl (not OSSearchAPIImpl directly) and setting Config.setProperty(MigrationPhase.FLAG_KEY, ...) per test, cleaning up in @After.

2. ES fallback in Phase 2

• When OSSearchAPIImpl throws, PhaseRouter.readChecked retries against ES.
• Requires simulating an OS failure (e.g. wrong index name) while ES is healthy.

3. searchRaw permission injection filters results for non-admin users

• Needs at least one indexed document + a non-admin user with explicit role/permission setup.
• executeSearch() lines 263–300 inject a permission filter; today this is untested end-to-end against OS.

Reference files

• SearchAPIImpl: dotCMS/src/main/java/com/dotcms/content/index/SearchAPIImpl.java
• PhaseRouter: dotCMS/src/main/java/com/dotcms/content/index/PhaseRouter.java
• OSSearchAPIImpl: dotCMS/src/main/java/com/dotcms/content/index/opensearch/OSSearchAPIImpl.java
• Phase config in tests: MigrationPhaseTest.java — Config.setProperty(MigrationPhase.FLAG_KEY, ...)
• Document indexing pattern: ContentletIndexOperationsOSIntegrationTest.java

Suggested class name

SearchAPIImplPhaseRoutingIT (requires both ES + OS containers, or a shared cluster with phase-switching)