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/api/src/handlers.rs

@@ -0,0 +1,26 @@
+use axum::{extract::State, Json};
+use std::sync::atomic::Ordering;
+
+use crate::{error::ApiError, state::AppState};
+
+pub async fn health() -> &'static str {
+    "ok"
+}
+
+pub async fn docs_redirect() -> impl axum::response::IntoResponse {
+    axum::response::Redirect::to("/swagger-ui/")
+}
+
+pub async fn ready(State(state): State<AppState>) -> Result<Json<serde_json::Value>, ApiError> {
+    sqlx::query("SELECT 1").execute(&state.pool).await?;
+    Ok(Json(serde_json::json!({"status": "ready"})))
+}
+
+pub async fn metrics(State(state): State<AppState>) -> String {
+    format!(
+        "requests_total {}\npage_cache_hits {}\npage_cache_misses {}\n",
+        state.metrics.requests_total.load(Ordering::Relaxed),
+        state.metrics.page_cache_hits.load(Ordering::Relaxed),
+        state.metrics.page_cache_misses.load(Ordering::Relaxed),
+    )
+}