feat(appview): profile cache + Jetstream indexing + denormalised counts

Adds the AppView-side half of the profile feature so non-local-PDS
authors also get their profile metadata indexed (the Jetstream
identity event stream only carries the handle, not display name /
bio / avatar). The PDS-push path was already wired by the previous
commit; this lands the Jetstream path.

Migration 0005:

* `profiles` table keyed by DID with display_name / description /
  avatar_cid / banner_cid plus denormalised post_count /
  follower_count / following_count. Backfilled from the posts
  table on apply.
* `posts.avatar_cid` column — populated from the profiles cache
  at `upsert_post` time so the PostCard can render an avatar
  inline without a per-row PDS round trip.

Migration 0007 (clean-up): the original 0005 also created a
`LOWER(handle)` index that no query uses; this drops it
idempotently so dev DBs that already applied 0005 converge.

Indexer (`crates/appview/src/indexer.rs`):

* New `app.bsky.actor.profile` arm in `apply_commit` calls
  `upsert_profile` on create, DELETEs the row on delete. Handle
  is looked up from `posts` (the Jetstream commit envelope
  doesn't carry it).
* `upsert_post` signature is now `&mut PostRow` so it can fill
  `row.avatar_cid` from the profiles cache; the ON CONFLICT
  clause uses `COALESCE(EXCLUDED, posts)` so re-indexing doesn't
  overwrite an already-known avatar.
* `upsert_profile` writes display_name / description /
  avatar_cid / banner_cid + the denormalised counts.
* `blob_link_of` helper accepts both `{ $type, ref.$link }`
  and legacy flat `{ $link }` blob-ref shapes.

Ingest (`crates/appview/src/ingest.rs`):

* `app.bsky.actor.profile` create/delete arms in the PDS-push
  path. The handle-fallback previously did `SELECT handle FROM
  users WHERE did = $1` — but the AppView has no `users` table
  (it's PDS-owned state). Replaced with a simple use-what-the-PDS-
  sent approach; the handle_sync worker fills the column later.

Routes (`crates/appview/src/routes.rs`):

* `resolve_profile` reads the denormalised profile fields from
  the cache. When no profile row exists the `post_count` fallback
  uses a live `SELECT COUNT(*)` instead of `posts.len()`, so
  prolific authors without a profile row report the real count
  rather than the 50-post slice cap.

Tests (DB-gated, run when DATABASE_URL_APPVIEW is set):

* `blob_link_of_modern_shape` / `_legacy_flat_link` /
  `_missing_field`.
* `upsert_profile_round_trip` — insert + replace semantics.
* `apply_commit_indexes_profile_create` — end-to-end Jetstream
  arm + delete.

crates/appview/src/routes/types.rs

@@ -54,6 +54,12 @@ pub struct PostRow {
     pub like_count: i64,
     #[serde(default)]
     pub repost_count: i64,
+    /// Resolved author-avatar CID from the `profiles` cache. NULL
+    /// until the user has pushed a profile through the PDS path. The
+    /// PostCard uses this to render an <Avatar cid={post.avatar_cid}/>
+    /// inline without a per-row PDS round trip.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub avatar_cid: Option<String>,
 }
 
 /// Raw `FromRow` impl — we read `embed` as the helper newtype then
@@ -76,6 +82,7 @@ impl<'r> FromRow<'r, sqlx::postgres::PgRow> for PostRow {
             created_at: row.try_get("created_at")?,
             like_count: row.try_get::<i64, _>("like_count").unwrap_or(0),
             repost_count: row.try_get::<i64, _>("repost_count").unwrap_or(0),
+            avatar_cid: row.try_get::<Option<String>, _>("avatar_cid").ok().flatten(),
         })
     }
 }
@@ -100,6 +107,8 @@ pub struct PostRowWithIndexed {
     pub indexed_at: DateTime<Utc>,
     pub like_count: i64,
     pub repost_count: i64,
+    /// Resolved author-avatar CID from the `profiles` cache.
+    pub avatar_cid: Option<String>,
 }
 
 impl<'r> FromRow<'r, sqlx::postgres::PgRow> for PostRowWithIndexed {
@@ -121,6 +130,7 @@ impl<'r> FromRow<'r, sqlx::postgres::PgRow> for PostRowWithIndexed {
             indexed_at: row.try_get("indexed_at")?,
             like_count: row.try_get::<i64, _>("like_count").unwrap_or(0),
             repost_count: row.try_get::<i64, _>("repost_count").unwrap_or(0),
+            avatar_cid: row.try_get::<Option<String>, _>("avatar_cid").ok().flatten(),
         })
     }
 }
@@ -142,6 +152,7 @@ impl From<PostRowWithIndexed> for PostRow {
             created_at: r.created_at,
             like_count: r.like_count,
             repost_count: r.repost_count,
+            avatar_cid: r.avatar_cid,
         }
     }
 }
@@ -162,6 +173,22 @@ pub struct ProfileResponse {
     pub posts: Vec<PostRow>,
     pub followers: i64,
     pub following: i64,
+    /// Denormalised profile metadata from the `profiles` cache.
+    /// Optional — populated when the user has a profile record
+    /// pushed to the AppView (PDS write or Jetstream `identity` event).
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub display_name: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub description: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub avatar_cid: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub banner_cid: Option<String>,
+    /// Denormalised count of the user's posts (computed by
+    /// `upsert_profile` from the `posts` table). Lets the
+    /// ProfileView-Page render without an extra `COUNT(*)`.
+    #[serde(default)]
+    pub post_count: i64,
 }
 
 /// `GET /api/search` response. `q` echoes the search string so the