docs: fix local dev setup instructions

[jack-piplabs]

Summary

• Add Node.js v18/20/22/24 as a prerequisite (Convex backend rejects v25+)
• Remove duplicate CONVEX_SITE_URL from .env.local example (Convex derives it from VITE_CONVEX_SITE_URL)
• Reorder setup steps so the Convex backend starts before auth/JWT configuration
• Add "Set backend environment variables" section explaining that AUTH_GITHUB_ID, AUTH_GITHUB_SECRET, and SITE_URL must be set via bunx convex env set, not just in .env.local
• Make frontend port explicit (bun run dev -- --port 3000) with a note about changing it
• Add updateGlobalStatsInternal step after seeding to refresh the cached skills count

Test plan

• Follow the updated CONTRIBUTING.md instructions from scratch on a clean checkout
• Verify bunx convex dev --typecheck=disable starts the backend
• Verify bunx convex env set commands configure auth correctly
• Verify GitHub OAuth login works after setting backend env vars
• Verify seeded skills appear with correct count after running updateGlobalStatsInternal

[vercel]

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[greptile-apps]

Greptile Summary

Improves the local development setup documentation with better prerequisite information, clearer environment variable handling, and more logical step ordering. Key improvements include:

• Adds Node.js version requirement (v18/20/22/24) upfront, noting v25+ incompatibility with Convex backend
• Reorders steps to start Convex backend before configuration (logical dependency flow)
• Clarifies that backend environment variables (AUTH_GITHUB_ID, AUTH_GITHUB_SECRET, SITE_URL) must be set via bunx convex env set separately from .env.local
• Makes frontend port explicit (--port 3000) with guidance on updating both frontend and backend URLs if changed
• Adds required updateGlobalStatsInternal step after seeding to refresh cached stats
• Removes duplicate CONVEX_SITE_URL from .env.local example (derived from VITE_CONVEX_SITE_URL)

All changes are documentation-only with no functional code modifications. The test plan confirms these instructions work end-to-end on a clean checkout.

Confidence Score: 5/5

• This PR is safe to merge with no risk - documentation-only changes that improve clarity and accuracy
• Score reflects that this is a documentation-only PR with no code changes, comprehensive testing (verified on clean checkout), and logical improvements that make the setup process clearer and more accurate for new contributors
• No files require special attention

_{Last reviewed commit: 22d55a9}