Add YAML form portability and validated MIO editing - #53

Forms can now be exported and imported as a complete, versioned YAML package, and MIO can create or update forms through a validated editing workflow. For example, MIO can create a contact form where selecting “Other” reveals a required text area, then offer Preview after the save is confirmed.

Changes

• Add YAML export, validation and draft import in the builder, a JSON Schema contract, a validation CLI, and authenticated REST endpoints. Packages include the form definition, its base theme plus changed tokens, per-form CSS overrides, embedded choice images and page references.
• Add private, window-scoped MIO tools backed by detailed linked Markdown documentation. Validation returns error paths and repair suggestions, permits two corrections, and requires a successful validation receipt before applying an edit.
• Preserve existing publication status and unrelated form configuration. Guard stale edits with revisions, record durable user-scoped operation receipts, and provide read-only reconciliation of uncertain saves.
• Offer a receipt-bound Preview action through the new optional MIO response-actions API. It opens the saved form without another save or AI request. Existing shells retain the manual workflows; assistant features depend on the compatible OpenStation API and user/provider configuration.
• Include API review and action-button handoff documents for the unmerged OpenStation PR #816, plus regression tests for both original and recovery API contracts.

Validation

• TypeScript and all 463 standard Vitest tests pass; the two optional conformance tests also pass against the actual sibling MIO source.
• The 20 focused WordPress assistant/package tests pass (200 assertions) on Docker port 8889.
• All four browser scenarios pass on Docker 8889: package round-trip, original MIO adapter, recovery adapter, and the real chat/Preview workflow. Provider replies are simulated; WordPress validation, saves and preview rendering are real.
• The 75 relevant upstream MIO tests pass against the developer's latest local fixes.
• PHPCS reports zero errors; the plugin ZIP and committed bundles rebuild successfully.
• The full local PHP run reproduces eight existing Gravity Forms/WPForms importer failures on the unchanged base commit as well. These are documented separately from the passing new-feature tests; GitHub CI subsequently passed the full PHPUnit and PHPCS job, along with JavaScript/bundle and ZIP checks.

Documentation

• YAML package format
• MIO knowledge index
• MIO API review and compatibility results
• Preview action proposal and implementation status