Studio Code: Extract local agent guidance into skills

[youknowriad]

Related issues

• N/A

How AI was used in this PR

Codex helped extract local agent guidance from the system prompt into focused skills while preserving the existing behavior and recommendation content. The changes were reviewed and verified with targeted prompt tests, typechecking, and related unit tests.

Proposed Changes

• Add a visual-design skill and route local site creation, redesign, layout, CSS, typography, color, motion, and polish work through it.
• Add a plugin-recommendations skill for general plugin choice guidance while preserving the existing Jetpack Forms, newsletter signup, Jetpack, and slideshow recommendations.
• Add a block-content skill for editable WordPress block markup, core/html limits, block-theme layout cascade rules, validation, and skeleton-first page/CSS recipes.
• Add a wpcom-remote-management skill for WordPress.com REST API namespace selection, endpoint guidance, response-size control, remote content/template/theme/plugin operations, and visual verification.
• Slim the local system prompt so it routes to skills instead of embedding the full design, plugin, and block-content recipes inline.
• Slim the remote WordPress.com system prompt so it keeps the hard site/plan safety rules inline while routing endpoint recipes to the new remote-management skill.
• Keep deterministic HTML block policy checks in code and point violations to the relevant skill.
• Add prompt coverage that verifies routed skill names exist in the bundled local skills directory.

Testing Instructions

• npx eslint --fix apps/cli/ai/system-prompt.ts apps/cli/ai/plugin-recommendations.ts apps/cli/ai/block-content-policy.ts apps/cli/ai/tests/system-prompt.test.ts
• npm run typecheck
• npm test -- apps/cli/ai/tests/system-prompt.test.ts apps/cli/ai/tests/block-content-policy.test.ts
• npm test -- apps/cli/ai/tests/system-prompt.test.ts

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing a39d22b vs trunk

app-size

Metric	trunk	a39d22b	Diff	Change
App Size (Mac)	1339.25 MB	1339.24 MB	0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	a39d22b	Diff	Change
load	1759 ms	1749 ms	10 ms	⚪ 0.0%

site-startup

Metric	trunk	a39d22b	Diff	Change
siteCreation	9624 ms	9589 ms	35 ms	⚪ 0.0%
siteStartup	4916 ms	4913 ms	3 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)