API Builder V1: Inspector + Advanced JSON panel with two-way sync

[nicdavidson]

Goal
Support both form-driven and engineering-driven editing in one interface.

Scope

• Right panel tabs: Inspector, Advanced JSON
• JSON tab edits execution_plan and response_mapping
• Two-way sync between structured controls and JSON
• Parse/validation errors inline

Acceptance Criteria

• JSON edits reflect in row preview immediately
• Form edits update JSON panel
• Invalid JSON blocks save with explicit error

[nicdavidson]

Implemented #497 on feature/add-api-builder and pushed.

What shipped

• Added right-side tabbed panel with:
  • Inspector tab (execution step preview + response field preview)
  • Advanced JSON tab (editable executionPlan + responseMapping)
• Wired two-way behavior:
  • Form/source edits continue regenerating JSON payloads.
  • JSON edits now immediately update Inspector previews.
• Added inline JSON validation errors (parse + object-shape validation) in Advanced JSON tab.
• Save/Create buttons are now blocked when JSON is invalid.

Validation

• npm run build passes.
• Existing repo baseline warnings still present (CommonJS + known lint baseline), no new blocking build failures.

Commit

• fb09b9cb — feat(api-builder): add inspector and advanced json side panel sync

Branch

• Pushed to origin/feature/add-api-builder.