feat: declare skills in workspace .boilerplate.json

[pyramation]

Summary

Declares the pgpm skill in the workspace template's .boilerplate.json. After pgpm init workspace scaffolds the project, the pgpm CLI reads this config and runs npx skills add to install the skill automatically.

"skills": [
  { "source": "constructive-io/constructive", "skills": ["pgpm"] }
]

Companion PRs:

• feat(pgpm): install skills from .boilerplate.json after scaffold constructive#1271 (merged) — pgpm CLI installSkills() consumer
• feat(genomic): add skills field to BoilerplateConfig dev-utils#87 — upstream BoilerplateSkill type in genomic

Link to Devin session: https://app.devin.ai/sessions/8a70e4bc95b947faa41db21e02ed818e
Requested by: @pyramation

[devin-ai-integration]

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