Add per-course content roots and course scaffold

[puppe1990]

Summary

• move course markdown content out of the shared docs root into courses//docs
• make VitePress resolve the active course content directory through srcDir
• add npm run course:new -- "Course Title" to scaffold a new course manifest and starter docs

Validation

• npm test
• npm run docs:build
• npm run course:activate -- agent-ops-bootcamp && npm run docs:build && npm run course:activate -- learn-harness-engineering
• npm run course:new -- sample-growth-lab "Sample Growth Lab" followed by activation + build, then cleanup

[chatgpt-codex-connector]

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