docs: establish contribution and product foundations

[pramodkandel]

What changed

Establishes the repository contribution and product foundations: contributor policies and conventions, English and Nepali project guidance, GitHub issue and pull-request templates, and the product requirements with v0.1 scope. Based on the original foundations work in devnepal-old#4.

Closes #41.

Contract impact

• No changes to packages/api-contract

Checks

• git diff --check origin/main...HEAD
• bun run lint
• bun run typecheck
• bun run test
• bun run api:check
• bun run build

The unchecked application checks were not run; this branch changes documentation and repository guidance only.

Notes for reviewers

Please review the contributor workflow and policies for consistency, and the product requirements as the intended specification rather than a claim that all requirements are implemented. No application UI changes; screenshots are not applicable.

Foundation checklist

• Commits signed off (git commit -s)
• Works in both English and Nepali where applicable
• No secrets or real personal data anywhere in the diff
• Documentation updated; English and Nepali versions agree where both exist