feat: implement merge readiness plan to close gaps between v2 and v1

- Task 1: Fix feed response hydration by adding `to_thought_response` helper and updating feed handlers to return full `ThoughtResponse`.
- Task 2: Wire follower/following REST routes for user feeds.
- Task 3: Add user listing and count endpoints, including `GET /users` and `GET /users/count`.
- Task 4: Implement popular tags feature with `GET /tags/popular`.
- Task 5: Enhance configuration with HOST, CORS_ORIGINS, and optional rate limiting using tower-governor.

crates/adapters/postgres/src/user.rs

@@ -1,15 +1,21 @@
 use async_trait::async_trait;
 use chrono::{DateTime, Utc};
-use sqlx::PgPool;
 use domain::{
     errors::DomainError,
     models::{feed::UserSummary, user::User},
     ports::UserRepository,
     value_objects::{Email, PasswordHash, UserId, Username},
 };
+use sqlx::PgPool;
 
-pub struct PgUserRepository { pool: PgPool }
-impl PgUserRepository { pub fn new(pool: PgPool) -> Self { Self { pool } } }
+pub struct PgUserRepository {
+    pool: PgPool,
+}
+impl PgUserRepository {
+    pub fn new(pool: PgPool) -> Self {
+        Self { pool }
+    }
+}
 
 #[derive(sqlx::FromRow)]
 pub(crate) struct UserRow {
@@ -120,7 +126,15 @@ impl UserRepository for PgUserRepository {
         .map(|_| ())
     }
 
-    async fn update_profile(&self, user_id: &UserId, display_name: Option<String>, bio: Option<String>, avatar_url: Option<String>, header_url: Option<String>, custom_css: Option<String>) -> Result<(), DomainError> {
+    async fn update_profile(
+        &self,
+        user_id: &UserId,
+        display_name: Option<String>,
+        bio: Option<String>,
+        avatar_url: Option<String>,
+        header_url: Option<String>,
+        custom_css: Option<String>,
+    ) -> Result<(), DomainError> {
         sqlx::query(
             "UPDATE users SET display_name=$2,bio=$3,avatar_url=$4,header_url=$5,custom_css=$6,updated_at=NOW() WHERE id=$1"
         )
@@ -159,22 +173,25 @@ impl UserRepository for PgUserRepository {
              LEFT JOIN follows f2 ON f2.follower_id=u.id AND f2.state='accepted'
              WHERE u.local=true
              GROUP BY u.id
-             ORDER BY u.username"
+             ORDER BY u.username",
         )
         .fetch_all(&self.pool)
         .await
         .map_err(|e| DomainError::Internal(e.to_string()))?;
 
-        Ok(rows.into_iter().map(|r| UserSummary {
-            id: UserId::from_uuid(r.id),
-            username: r.username,
-            display_name: r.display_name,
-            avatar_url: r.avatar_url,
-            bio: r.bio,
-            thought_count: r.thought_count,
-            follower_count: r.follower_count,
-            following_count: r.following_count,
-        }).collect())
+        Ok(rows
+            .into_iter()
+            .map(|r| UserSummary {
+                id: UserId::from_uuid(r.id),
+                username: r.username,
+                display_name: r.display_name,
+                avatar_url: r.avatar_url,
+                bio: r.bio,
+                thought_count: r.thought_count,
+                follower_count: r.follower_count,
+                following_count: r.following_count,
+            })
+            .collect())
     }
 
     async fn count(&self) -> Result<i64, DomainError> {
@@ -208,7 +225,10 @@ mod tests {
     #[sqlx::test(migrations = "./migrations")]
     async fn find_by_username_returns_none_when_missing(pool: sqlx::PgPool) {
         let repo = PgUserRepository::new(pool);
-        let result = repo.find_by_username(&Username::new("ghost").unwrap()).await.unwrap();
+        let result = repo
+            .find_by_username(&Username::new("ghost").unwrap())
+            .await
+            .unwrap();
         assert!(result.is_none());
     }
 
@@ -222,7 +242,10 @@ mod tests {
             PasswordHash("hash".into()),
         );
         repo.save(&user).await.unwrap();
-        let found = repo.find_by_email(&Email::new("bob@ex.com").unwrap()).await.unwrap();
+        let found = repo
+            .find_by_email(&Email::new("bob@ex.com").unwrap())
+            .await
+            .unwrap();
         assert!(found.is_some());
     }
 
@@ -236,7 +259,16 @@ mod tests {
             PasswordHash("hash".into()),
         );
         repo.save(&user).await.unwrap();
-        repo.update_profile(&user.id, Some("Charlie".into()), Some("bio".into()), None, None, None).await.unwrap();
+        repo.update_profile(
+            &user.id,
+            Some("Charlie".into()),
+            Some("bio".into()),
+            None,
+            None,
+            None,
+        )
+        .await
+        .unwrap();
         let found = repo.find_by_id(&user.id).await.unwrap().unwrap();
         assert_eq!(found.display_name.as_deref(), Some("Charlie"));
         assert_eq!(found.bio.as_deref(), Some("bio"));