backend(features): quota enforcement, PIN reset, /me, original download, toggles

- handlers/me.rs (new): GET /api/v1/me/context (profile + role + privacy_note
  + quota toggle state, fetched once on app bootstrap) and GET /api/v1/me/quota
  (live used / limit / active uploaders / free disk).
- handlers/upload.rs:
  - quota enforcement via the dynamic formula
    floor((free_disk * tolerance) / max(active_uploaders, 1)),
    gated by quota_enabled + storage_quota_enabled toggles
  - new GET /api/v1/upload/{id}/original — unauthed by design
    (matches /media/previews/* — URL is the secret) so it works as
    <img src> / <video src> / window.open
  - rate-limit toggle wiring (rate_limits_enabled + upload_rate_enabled)
- handlers/host.rs:
  - POST /api/v1/host/users/{id}/pin-reset — Host may reset guest PINs,
    Admin may reset guest + host PINs (never another admin or self).
    Returns the freshly-generated plaintext PIN once; emits a global
    pin-reset SSE so the affected user's device can clear its localStorage.
  - set_role guard expanded so hosts can demote other hosts (not self,
    never admins) — backend match for the doc'd permission model.
- handlers/admin.rs: ALLOWED_KEYS split into NUMERIC_KEYS / BOOL_KEYS /
  TEXT_KEYS with per-kind validation; saving privacy_note broadcasts an
  event-updated SSE so other clients refresh live.
- handlers/feed.rs, handlers/admin.rs (export), auth/handlers.rs:
  rate-limit toggle wiring at every limiter call site.
- auth/handlers.rs: when an expired PIN lockout is detected on /recover,
  reset failed_pin_attempts to zero before the bcrypt check — without
  this every wrong PIN re-locked the user after the cooldown.
- main.rs: wire startup_recovery + spawn_periodic_tasks, register the
  new /me/context, /me/quota, /upload/{id}/original, and
  /host/users/{id}/pin-reset routes.

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

backend/src/handlers/feed.rs

@@ -9,6 +9,7 @@ use uuid::Uuid;
 
 use crate::auth::middleware::AuthUser;
 use crate::error::AppError;
+use crate::services::config;
 use crate::services::rate_limiter::client_ip;
 use crate::state::AppState;
 
@@ -61,9 +62,19 @@ pub async fn feed(
     Query(q): Query<FeedQuery>,
 ) -> Result<Json<FeedResponse>, AppError> {
     let ip = client_ip(&headers, "unknown");
-    let rate_limit = get_config_usize(&state.pool, "feed_rate_per_min", 60).await;
-    if !state.rate_limiter.check(format!("feed:{ip}"), rate_limit, Duration::from_secs(60)) {
-        return Err(AppError::TooManyRequests("Zu viele Anfragen. Bitte warte kurz und versuche es erneut.".into(), None));
+    let rate_limits_on = config::get_bool(&state.pool, "rate_limits_enabled", true).await;
+    let feed_rate_on = config::get_bool(&state.pool, "feed_rate_enabled", true).await;
+    if rate_limits_on && feed_rate_on {
+        let rate_limit = config::get_usize(&state.pool, "feed_rate_per_min", 60).await;
+        if !state
+            .rate_limiter
+            .check(format!("feed:{ip}"), rate_limit, Duration::from_secs(60))
+        {
+            return Err(AppError::TooManyRequests(
+                "Zu viele Anfragen. Bitte warte kurz und versuche es erneut.".into(),
+                None,
+            ));
+        }
     }
 
     let limit = q.limit.unwrap_or(20).min(100);
@@ -238,16 +249,6 @@ pub async fn hashtags(
     ))
 }
 
-async fn get_config_usize(pool: &sqlx::PgPool, key: &str, default: usize) -> usize {
-    let row: Option<(String,)> =
-        sqlx::query_as("SELECT value FROM config WHERE key = $1")
-            .bind(key)
-            .fetch_optional(pool)
-            .await
-            .unwrap_or(None);
-    row.and_then(|r| r.0.parse().ok()).unwrap_or(default)
-}
-
 async fn get_cursor_time(pool: &sqlx::PgPool, cursor_id: Uuid) -> Option<DateTime<Utc>> {
     let row: Option<(DateTime<Utc>,)> =
         sqlx::query_as("SELECT created_at FROM upload WHERE id = $1")