[TASK] Phase-aware routing integration tests for @IndexRouter classes

Description

ESContentFactoryImpl, ESMappingAPIImpl, and IndexAPIImpl are annotated @IndexRouter — they act as coordinators that dispatch to ES and/or OS delegates depending on the active MigrationPhase.

The existing integration test suites (ESContentFactoryImplTest, ESMappingAPITest, ContentletIndexAPIImplTest) cover ES-only behaviour (Phase 0 implicitly). There are no tests that verify routing decisions across the 4 migration phases.

Routing table under test

Acceptance Criteria

• Extend existing tests where feasible; do not rewrite full test classes.
• For each router class, select the public methods that most clearly exercise routing (e.g. indexing a document, querying by index name) and parameterize them over all 4 phases.
• Each test scenario must:
  1. Set the active MigrationPhase to the target phase (via feature-flag override).
  2. Use two indices with different names (e.g. live_<runId> and working_<runId>).
  3. Call a public method that accepts one of the valid index names.
  4. Assert that the correct delegate(s) received the operation (spy/verify or count-based assertion on each index).
• Dual-write phases (1 and 2) must confirm the operation was applied to both indices.
• Read phases: confirm that the query result originates from the expected provider (ES in phases 0/1, OS in phases 2/3).
• Phase teardown must restore the original phase value and clean up test indices.
• Tests that require a live OS instance must be registered in OpenSearchUpgradeSuite; tests that can run ES-only belong in the standard suite.

Additional Context

• IndexConfigHelper.MigrationPhase.current() reads from a feature flag — use Config overrides or a test-only setter to control the phase in tests.

• Target classes: ESContentFactoryImpl (lines ~132, ~233-263), ESMappingAPIImpl, IndexAPIImpl.

• Related issues: #34931 (routing logic task), #35278 (OS delegate coverage).

• Run command:
  ```

  Phase 0/1-only scenarios (ES suite):

  ./mvnw verify -pl :dotcms-integration -Dcoreit.test.skip=false -Dit.test=ESContentFactoryImplTest

  Phases 1-3 (requires OS container):

  ./mvnw verify -pl :dotcms-integration -Dcoreit.test.skip=false -Dopensearch.upgrade.test=true
  ```

Start with ESContentFactoryImplTest, ESMappingAPITest, and ContentletIndexAPIImplTest, then inspect ESContentFactoryImpl, ESMappingAPIImpl, and IndexAPIImpl at the referenced routing points. Run the listed integration-test commands and use the feature-flag phase override while parameterizing scenarios across all four MigrationPhase values. Done means delegate reads and writes match the routing table, dual writes reach both indices, teardown restores the phase, and OS-dependent tests are registered in OpenSearchUpgradeSuite.