feat: integrate Skill assisted generation

[YYH211]

Summary

• Initialize newly created Skill apps with a blank workspace instead of generating a default SKILL.md from requirements.
• Add runtime support for syncing pro built-in skills into the sandbox home directory.
• Update workspace packaging and validation around skills/ directories and SKILL.md requirements.

Test

• pnpm exec vitest run -c vitest.config.ts test/core/ai/skill/builtinRuntime.test.ts test/core/ai/skill/editSandboxPackage.test.ts test/core/ai/skill/zipBuilder.test.ts
• git diff --check upstream/main...HEAD

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	15.72%	1328 / 8444
🔵	Statements	15.65%	1386 / 8852
🔵	Functions	13.76%	277 / 2012
🔵	Branches	12.9%	600 / 4650

File Coverage

No changed files found.

Generated in workflow #969 for commit 202683a by the Vitest Coverage Report Action

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