Install dependencies before Docs Agent verification

[chubes4]

Summary

• Install target repository dependencies before Docs Agent verification commands run.
• Applies the same setup to both developer docs and skills maintenance workflows so fresh runner workspaces can execute pnpm build and pnpm verify.

Testing

• pnpm install --frozen-lockfile && pnpm build && pnpm verify

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Diagnosed the workflow verification failure and drafted the minimal workflow change; Chris remains responsible for review and merge.