Declare forms capability for fixture 37

[chubes4]

Summary

• declare the forms capability for fixture 37
• allow the fixture matrix to provision Jetpack and run provider readiness

Verification

• cd php-transformer && composer test:canonical
• Jetpack-backed fixture matrix evidence is still required before this leaves draft

Part of #700.

AI assistance

GPT-5.6 Sol via OpenCode reviewed the fixture contract, made the metadata change, and ran the canonical verification. Chris Huber remains responsible for every line.

[chubes4]

Runtime verification is complete, but this remains draft because the full #700 gate is not green.

Homeboy run: 91572cd2-b045-47a9-b595-b40e331f23a9
Reproduction: homeboy runs show 91572cd2-b045-47a9-b595-b40e331f23a9
Transformer: 476a250517331871e4b5803eb401de082a44b385 (this PR combined with #706 for fixture proof)

Confirmed:

• Jetpack provisioning succeeded.
• Forms module preflight returned jetpack-forms-activated.
• Provider readiness returned jetpack-ready.
• Import validation passed.
• All 9 form findings are classified as native_conversion; Jetpack form/field blocks are registered in the editor.
• 7 pages were imported with zero core/html blocks.

Remaining blockers:

• All 7 visual comparisons differ (3.14% to 57.77% overlap mismatch).
• 6 editor surfaces are clean; current-exhibition reports one invalid-block warning.
• SSI currently fails to project the completed browser artifacts into its top-level fixture result, despite the files being present under the WP Codebox artifact tree.

The metadata change is correct and provider materialization works, but visual/editor parity still needs repair before this PR leaves draft.

[chubes4]

Closing as superseded by the corrected architecture. Fixture capabilities must remain metadata-only and must not provision Jetpack. The branch now has zero net changes after commit 7e65343c removes the declaration.

Replacement implementation:

• Emit editor-valid Jetpack form block trees static-site-importer#739 fixes Jetpack form serialization.
• Keep fixture capabilities metadata-only static-site-importer#740 removes capability-driven provider setup and proves SSI infers forms from arbitrary HTML.
• Homeboy run 0e7f3aab-18b7-4746-a428-1b0f6c8084a2 passed SSI import and all Jetpack block validation with fixture 37 declaring no capabilities.