fix(appview): populate handle from PDS ingest + backfill race-safely

The AppView side of the PDS→AppView ingest path. Receives the
optional 'handle' the PDS now ships, writes it onto the post row
on insert (with the existing 'COALESCE(NULLIF(\"`\"), handle)'
guard so an empty value never clobbers a previously-backfilled
handle).

The indexer's 'from_record' constructor gains an optional
'pds_handle' parameter so the same code path serves both the
Jetstream ingest (where handle is absent by protocol design)
and the local-PDS push (where handle is authoritative).

Updates the 5 existing test call sites + adjusts the 2-step
Jetstream handling flow to match. The unit/integration tests
that assert the post-shape on real Bluesky docs still pass.

crates/appview/src/ingest.rs

@@ -30,6 +30,13 @@ use tracing::{info, warn};
 #[derive(Debug, Deserialize)]
 pub struct IngestCommitReq {
     pub did: String,
+    /// The poster's current handle, as known by the PDS `users` table.
+    /// Optional in the wire payload — the AppView falls back to an
+    /// empty string, and the upsert COALESCE guard prevents the empty
+    /// value from clobbering a backfilled handle from the Jetstream
+    /// `identity` event path.
+    #[serde(default)]
+    pub handle: Option<String>,
     pub collection: String,
     pub action: String,
     pub rkey: String,
@@ -127,6 +134,7 @@ async fn apply(
                 &req.collection,
                 &cid,
                 &record,
+                req.handle.as_deref(),
             );
             indexer::upsert_post(&state.db, &row).await.map_err(db_err)?;
             Ok(true)