refactor: update AppState references to use state module

- Change all instances of AppState to reference the new state module across multiple files for consistency.
- Clean up imports in auth, books, index_jobs, libraries, pages, search, settings, thumbnails, and tokens modules.
- Simplify main.rs by removing unused code and organizing middleware and route handlers under the new handlers module.

apps/indexer/src/api.rs

@@ -0,0 +1,16 @@
+use axum::{extract::State, http::StatusCode, Json};
+use serde_json;
+
+use crate::AppState;
+
+pub async fn health() -> &'static str {
+    "ok"
+}
+
+pub async fn ready(State(state): State<AppState>) -> Result<Json<serde_json::Value>, StatusCode> {
+    sqlx::query("SELECT 1")
+        .execute(&state.pool)
+        .await
+        .map_err(|_| StatusCode::SERVICE_UNAVAILABLE)?;
+    Ok(Json(serde_json::json!({"status": "ready"})))
+}