[codex] Add delivery retry and tombstone proof

[Jess Sullivan (Jesssullivan)]

Summary

• add structured delivery log entries and deterministic queue processing for controlled retry evidence
• fix retry scheduling so pending tasks wait until nextRetryAt and failed tasks are not retried
• add reusable Tombstone delete activity construction and validation
• extend the controlled-peer proof to cover signed Delete/Tombstone and retry log evidence
• bump tummycrypt_tinyland_activitypub to 0.2.5

Validation

• pnpm install --frozen-lockfile
• pnpm test
• pnpm typecheck
• pnpm build
• pnpm check:package
• bazel build //...
• bazel test //...
• git diff --check