feat(dashboard): redesign homepage

[shmlkv]

Summary

• Redesigns the dashboard homepage hero around a local-first sovereign agent network message.
• Adds a live node mesh visual, signed identity panel, and network principle markers.
• Updates the document title to network.self.md — sovereign agent network.
• Improves secondary text contrast and keeps homepage grid cards sized to their content.

Verification

• pnpm build
• pnpm test
• pnpm --filter @networkselfmd/dashboard build
• pnpm --filter @networkselfmd/dashboard test
• Browser smoke test at / with no console errors.

Scope

• Dashboard homepage presentation only; no backend/API behavior changes.
• Existing unrelated worktree changes were left untouched in the original checkout.