fix: replace repo_sync_index wiring with purgatory announcement sync timer

Instead of threading repo_sync_index through PolicyContext/builder.rs/main.rs
to handle user-submitted purgatory announcements, add a simple background
timer (run_purgatory_announcement_sync, every 5s) that scans the purgatory
for announcement entries and registers them in repo_sync_index as StateOnly.

This is simpler and covers both flows:
- Sync-path announcements: inline registration still happens during event
  processing (sync/mod.rs:1839+), timer provides a safety net
- User-submitted announcements: SelfSubscriber never sees them (rejected
  from DB), timer is the primary registration path

The timer calls sync_purgatory_announcements_to_index() which:
1. Snapshots purgatory via new announcements_for_sync() public method
2. Or_inserts StateOnly entries (never downgrades Full entries)
3. Detects newly added relay URLs and calls handle_new_sync_filters to
   connect and subscribe - fixing the failing test that expected relay
   discovery from a user-submitted purgatory announcement

Removes: repo_sync_index field from PolicyContext, set/get_repo_sync_index
methods, set_repo_sync_index on Nip34WritePolicy, wiring in main.rs, and
the inline AcceptPurgatory registration block in builder.rs.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/purgatory/mod.rs b/src/purgatory/mod.rs
index 3b5514b..1894738 100644
--- a/src/purgatory/mod.rs
+++ b/src/purgatory/mod.rs
@@ -680,6 +680,23 @@ impl Purgatory {
         self.announcement_purgatory.len()
     }
 
+    /// Collect (repo_id, relay_urls) for all announcements currently in purgatory.
+    ///
+    /// Returns a vec of `(repo_id, relay_urls)` where `repo_id` is the addressable
+    /// coordinate string `"30617:{pubkey_hex}:{identifier}"`. Used by the purgatory
+    /// announcement sync timer to register StateOnly entries in `repo_sync_index`.
+    pub fn announcements_for_sync(&self) -> Vec<(String, HashSet<String>)> {
+        self.announcement_purgatory
+            .iter()
+            .map(|entry| {
+                let (owner, identifier) = entry.key();
+                let repo_id = format!("30617:{}:{}", owner.to_hex(), identifier);
+                let relays = entry.value().relays.clone();
+                (repo_id, relays)
+            })
+            .collect()
+    }
+
     /// Get all event IDs currently stored in purgatory AND previously expired events.
     ///
     /// Returns a HashSet of all event IDs for: