feat: add durable guest reconnect authorization foundation

[jiashuoz]

A surviving microVM guest currently cannot reconnect safely: the original bootstrap is single-use, and a signature alone would not fence replaced runners or replayed attempts. This adds the authorization foundation for reconnect: a canonical Ed25519 transcript, original runner-connection generation on session requests, and a control application service backed by atomic PostgreSQL enrollment and one-shot challenge consumption.

The store checks current placement and connected runner generation while holding authority locks, checks expiry against database time, and atomically advances a connection epoch and replaces the bootstrap hash. Cold bootstrap minting invalidates guest enrollment. No private key or RAM is persisted.

This draft does not enable reconnect, advertise a capability, expose reconnect RPCs, change guest behavior, or recover listeners. Hosted support, guest/runner handshakes, immediate relay fencing, and live KVM qualification remain on this branch's integration roadmap. The implemented contract and remaining gates are in docs/design/2026-09-29-guest-reconnect-authorization.md.

Validation:

• Real PostgreSQL tests cover concurrent consumption (one winner), durable replay rejection, wrong key/session/boot/scope, expiry, stale runner generation, and cold-boot invalidation.
• Golden transcript/signature tests and actual WebSocket generation-binding regression pass.
• A separately built example against disposable PostgreSQL passes enrollment, proof, fresh-bootstrap redemption and replay refusal.
• make verify passes with real PostgreSQL and Docker integration explicitly disabled. The initial unrestricted run encountered local Docker credential-helper/registry failures and a timing-sensitive CLI test; the CLI test passed in the rerun. This is not a local Docker qualification.
• Independent and adversarial reviews complete, with no remaining findings. Added a reusable store conformance suite, lifecycle/pending-attempt/capability preservation regressions, and a synchronized database lock-wait expiry test; clarified that preliminary proof reads are not authorization.
• Focused race checks pass for protocol, runner plane and PostgreSQL. The standalone real-database example was repeated successfully after review updates.

Final commit 8c953fc: GitHub Actions verify passed (run 36581396796). Disposable local database and example binary removed; root checkouts preserved.