feat: announcement purgatory

Extends purgatory to hold repository announcements until git data arrives,
preventing empty repositories from being served to clients.

When an announcement is received, a bare repo is created immediately and the
announcement is held in purgatory. It is only promoted and served once a git
push confirms real content exists. If no push arrives before expiry, the bare
repo is deleted and the announcement is silently discarded.

Key behaviours:
- Soft expiry: announcements are hidden from clients but kept alive while git
  pushes are in progress, reviving on successful push
- Expiry is extended when a matching state event or git push is observed
- NIP-09 deletion events remove announcements from purgatory
- Purgatory state (announcements, state events, PR events, expired set) is
  persisted to disk on graceful shutdown and restored on startup, with elapsed
  downtime subtracted from expiry deadlines
- Purgatory announcements drive StateOnly sync in the sync system so state
  events are fetched from listed relays before promotion
- SyncLevel added to RepoSyncIndex to distinguish purgatory repos (StateOnly)
  from promoted repos (Full L2+L3 sync)

1 files changed, 2 insertions, 0 deletions

diff --git a/src/nostr/policy/mod.rs b/src/nostr/policy/mod.rs
index 1566b6c..f5b981a 100644
--- a/src/nostr/policy/mod.rs
+++ b/src/nostr/policy/mod.rs
@@ -6,11 +6,13 @@
 /// - `PrEventPolicy` - PR/PR Update validation
 /// - `RelatedEventPolicy` - Forward/backward reference checking
 mod announcement;
+mod deletion;
 mod pr_event;
 mod related;
 mod state;
 
 pub use announcement::{AnnouncementPolicy, AnnouncementResult};
+pub use deletion::DeletionPolicy;
 pub use pr_event::PrEventPolicy;
 pub use related::{ReferenceResult, RelatedEventPolicy};
 pub use state::{StatePolicy, StateResult};