chore: adopt current Loaf working model

[levifig]

Summary

Establish the current Loaf project operating model before active development.

• Add tracked project instructions, Loaf configuration, knowledge scaffolding, and compatibility links.
• Define the approved vision, strategy, and technology-neutral architecture.
• Move branch guidance to main plus short-lived Change branches while preserving legacy planning context.
• Document reproducible local verification and safe development configuration.

Test plan

• pnpm install --frozen-lockfile
• pnpm types
• Frontend and backend TypeScript checks
• pnpm build
• pnpm test (181 tests)
• Loaf configuration, state, doctor, and knowledge-base checks