Consume Agents API as a plugin dependency

[chubes4]

Summary

• Require the agents-api plugin at runtime instead of bootstrapping the Composer-vendored plugin fallback from Data Machine.
• Move automattic/agents-api to Composer require-dev and update the lockfile to the merged WP_Agent_* contracts.
• Align Data Machine adapters, docs, and tests with the current Agents API contract names and add Homeboy validation dependency resolution for agents-api.

Testing

• homeboy test data-machine --force-hot before rebase: 1206 passed, 3 skipped.
• homeboy test data-machine --force-hot after rebase: fails with 1 inherited ImageGenerationPromptRefinementTest::test_refine_prompt_includes_post_context_when_provided failure.
• Checked primary main with Homeboy and confirmed the same image prompt test fails there too, so it is not introduced by this branch.
• git diff --check origin/main...HEAD
• Verified no Extra-Chill/agents-api or extra-chill/agents-api references remain in this branch.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Updating the Data Machine dependency boundary and contract names, running local verification, and drafting this PR summary. Chris remains responsible for review and merge.

[homeboy-ci]

Homeboy Results — data-machine

Lint

✅ lint — passed

ℹ️ Full options: homeboy docs commands/lint
Deep dive: homeboy lint data-machine --changed-since f117c0d

Test

✅ test — passed

• 1170 passed
• 3 skipped

ℹ️ Auto-fix lint issues: homeboy refactor data-machine --from lint --write
ℹ️ Collect coverage: homeboy test data-machine --coverage
ℹ️ Save test baseline: homeboy test data-machine --baseline
ℹ️ Pass args to test runner: homeboy test -- [args]
ℹ️ Full options: homeboy docs commands/test
Deep dive: homeboy test data-machine --changed-since f117c0d

Audit

✅ audit — passed

• test_coverage — 355 finding(s)
• dead_code — 201 finding(s)
• intra-method-duplication — 71 finding(s)
• docs — 68 finding(s)
• requested_detectors — 34 finding(s)
• parallel-implementation — 33 finding(s)
• repeated_literal_shape — 13 finding(s)
• dead_guard — 10 finding(s)
• field_patterns — 5 finding(s)
• Abilities — 4 finding(s)
• Total: 815 finding(s)

Deep dive: homeboy audit data-machine --changed-since f117c0d

Tooling versions

• Homeboy CLI: homeboy 0.157.1+75e13968
• Extension: wordpress from https://github.com/Extra-Chill/homeboy-extensions
• Extension revision: a9f3e87
• Action: Extra-Chill/homeboy-action@v2