Prove project recommendation value

[sarthakagrawal927]

Summary

• make public project preview the first-value path
• retrieve similar projects from the eligible catalog with grounded tool evidence
• add the bounded GitHub repository picker and project-aware sign-in handoff
• replace digest-era analytics and update product, architecture, agent, and status documentation

Product impact

Guests can test Starboard with a public repository before signing in. Connected projects use similar repositories as the grounding set for explained tool recommendations, without adding billing or broader GitHub permissions.

Validation

• pnpm test: 35 files, 169 tests passed
• pnpm typecheck
• pnpm lint
• pnpm docs:check
• strict OpenSpec change and canonical spec validation
• pnpm build:cf
• git diff --check
• source design critique 36/40, audit 18/20, zero P0/P1

Follow-up evidence

The native in-app browser was unavailable, so fresh 390/768/1440 captures remain open in the active OpenSpec change. The existing valid design receipt still passes.