fix(reembed): set a busy timeout so it can run beside the live server

The tool opened a bare connection, so an UPDATE that met the server's
watcher holding the write lock failed at once (SQLITE_BUSY) and aborted
the whole run. Wait up to 15 s instead, like the server's own pool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/bin/reembed_embeddings.rs

@@ -286,6 +286,13 @@ async fn main() -> Result<()> {
 
     let mut conn = SqliteConnection::establish(&database_url)
         .with_context(|| format!("connecting to {}", database_url))?;
+    // Run beside the live server: its watcher writes the same file, and
+    // without a busy timeout one contended UPDATE fails the whole run.
+    {
+        use diesel::connection::SimpleConnection;
+        conn.batch_execute("PRAGMA busy_timeout = 15000;")
+            .context("setting busy_timeout")?;
+    }
 
     // This tool exists to move the corpus to the configured contract, so it
     // embeds even while the stored one differs (#189).