feat(migrate): add content_tsv backfill migration for full-text search

Populate content_tsv column on existing messages for PostgreSQL FTS support.

libs/migrate/lib.rs

@@ -3,6 +3,7 @@ pub use sea_orm_migration::prelude::*;
 mod m20260420_000003_add_model_id_to_room_message;
 pub mod m20260421_000001_add_agent_type_to_room_ai;
 pub mod m20260426_000001_add_thinking_content_to_room_message;
+pub mod m20260428_000001_backfill_content_tsv;
 
 pub async fn execute_sql(manager: &SchemaManager<'_>, sql: &str) -> Result<(), DbErr> {
     for stmt in split_sql_statements(sql) {
@@ -91,6 +92,7 @@ impl MigratorTrait for Migrator {
             Box::new(m20260420_000003_add_model_id_to_room_message::Migration),
             Box::new(m20260421_000001_add_agent_type_to_room_ai::Migration),
             Box::new(m20260426_000001_add_thinking_content_to_room_message::Migration),
+            Box::new(m20260428_000001_backfill_content_tsv::Migration),
             // Repo tables
             Box::new(m20250628_000028_create_repo::Migration),
             Box::new(m20250628_000029_create_repo_branch::Migration),

libs/migrate/m20260428_000001_backfill_content_tsv.rs

@@ -0,0 +1,17 @@
+use sea_orm_migration::prelude::*;
+
+#[derive(DeriveMigrationName)]
+pub struct Migration;
+
+#[async_trait::async_trait]
+impl MigrationTrait for Migration {
+    async fn up(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        let sql = include_str!("sql/m20260428_000001_backfill_content_tsv.sql");
+        super::execute_sql(manager, sql).await
+    }
+
+    async fn down(&self, _manager: &SchemaManager) -> Result<(), DbErr> {
+        // No-op: backfill is idempotent and non-reversible
+        Ok(())
+    }
+}

libs/migrate/sql/m20260428_000001_backfill_content_tsv.sql

@@ -0,0 +1,3 @@
+-- Backfill content_tsv for existing messages where it's NULL
+-- New messages are already handled by application code (connection.rs bulk insert)
+UPDATE room_message SET content_tsv = to_tsvector('simple', content) WHERE content_tsv IS NULL;