fix(appview): resolve_profile also looks up DID in profiles cache

A user who set their profile via the PDS push path before
posting anything has a row in `profiles` but no rows in
`posts` — the handle→DID lookup in `resolve_profile` only
checked `posts`, so the route synthesised an empty profile
(`did: ""`) for these users.

The fix: query `profiles` first, fall back to `posts` only
when there's no profile row. The new query uses
`LOWER(handle) = LOWER($1)` against the
`profiles_handle_idx` index (which is therefore no longer
dead weight and stays in 0005; 0007 still drops it idempotently
in case future edits reintroduce the original 'only-by-DID'
pattern).

Verified end-to-end against a running dev stack:
`GET /api/profile/<handle>` now returns the user's profile
metadata even when they have no posts indexed yet.

crates/appview/src/routes.rs

@@ -343,13 +343,31 @@ async fn resolve_profile(
         // Order by `indexed_at DESC` so we get the most recent DID for
         // this handle (a single user can re-use a handle if account
         // history allows, but the latest is the active one).
-        sqlx::query_scalar::<_, String>(
-            "SELECT did FROM posts WHERE handle = $1 ORDER BY indexed_at DESC LIMIT 1",
+        //
+        // Prefer the `profiles` cache over `posts` — a user can have
+        // a profile row (set via PDS push before posting) but no posts
+        // yet, and we want the profile page to render with the right
+        // DID rather than synthesise an empty one.
+        let row = sqlx::query_scalar::<_, String>(
+            "SELECT did FROM profiles WHERE LOWER(handle) = LOWER($1) \
+             ORDER BY indexed_at DESC LIMIT 1",
         )
         .bind(h)
         .fetch_optional(&state.db)
         .await
-        .map_err(db_err)?
+        .map_err(db_err)?;
+        if row.is_some() {
+            row
+        } else {
+            sqlx::query_scalar::<_, String>(
+                "SELECT did FROM posts WHERE handle = $1 \
+                 ORDER BY indexed_at DESC LIMIT 1",
+            )
+            .bind(h)
+            .fetch_optional(&state.db)
+            .await
+            .map_err(db_err)?
+        }
     } else {
         None
     };

migrations/appview/0005_profiles.sql

@@ -40,6 +40,7 @@ CREATE TABLE profiles (
     following_count    BIGINT NOT NULL DEFAULT 0,
     indexed_at         TIMESTAMPTZ NOT NULL DEFAULT now()
 );
+CREATE INDEX profiles_handle_idx ON profiles (LOWER(handle));
 CREATE INDEX profiles_indexed_at_idx ON profiles (indexed_at DESC);
 
 -- Backfill: seed a profile row for every handle we've already