sqlite: enable WAL + busy_timeout in connect(); 408/413/429 transient

The DB connection helper now sets `journal_mode=WAL`, `busy_timeout=5000`,
and `synchronous=NORMAL` on every connection. 13+ DAOs each open their
own connection through this helper and share one SQLite file — without
WAL, a writer's exclusive lock blocks readers and `load_persons` racing
the face-watch write storm errored instantly with "database is locked".
GPU face inference made this visible by speeding detect ~10× and
flooding the writer side. WAL persists in the file once set so the
debug binaries that bypass connect() inherit it automatically.

Also widen face_client.rs's classifier: 408 / 413 / 429 are now Transient
instead of Permanent. These are operator-fixable proxy/infra errors;
marking them Permanent poisons every affected photo with status='failed'
and requires manual SQL to recover. Specifically, Apollo's nginx
defaulted to a 1 MB body cap and silently rejected normal-size photos
before they reached the backend — the deferred-and-retry contract is
the right behavior for that class of fault.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/database/mod.rs

@@ -125,7 +125,24 @@ impl UserDao for SqliteUserDao {
 
 pub fn connect() -> SqliteConnection {
     let db_url = dotenv::var("DATABASE_URL").expect("DATABASE_URL must be set");
-    SqliteConnection::establish(&db_url).expect("Error connecting to DB")
+    let mut conn = SqliteConnection::establish(&db_url).expect("Error connecting to DB");
+    // Each DAO opens its own connection (13+ across the app) and they all
+    // share one DB file. Without WAL, a writer holds an exclusive lock
+    // that blocks readers — `load_persons` racing the face-watch write
+    // storm errors instantly with `database is locked`. WAL lets readers
+    // and one writer coexist; busy_timeout makes any remaining
+    // writer-vs-writer contention wait instead of failing fast.
+    // synchronous=NORMAL is the standard WAL pairing (FULL is for
+    // rollback-journal durability; we accept the narrow last-fsync
+    // window for the 2–10× write throughput).
+    use diesel::connection::SimpleConnection;
+    conn.batch_execute(
+        "PRAGMA journal_mode = WAL; \
+         PRAGMA busy_timeout = 5000; \
+         PRAGMA synchronous = NORMAL;",
+    )
+    .expect("set sqlite pragmas");
+    conn
 }
 
 #[derive(Debug)]