feat(downloads): WiFi-only network-type-aware download gating

Add a metered/cellular network detector so downloads honour a "WiFi
only" preference. Android reports network type via NetworkTypeMonitor;
Rust exposes it through download/network.rs and holds the queue pump when
on a metered connection, emitting a queue-wide waitingForNetwork event.
The frontend surfaces this via the networkType service and a
waitingForNetwork store flag.

TRACES: UR-053 | DR-074

src-tauri/src/download/cache.rs

@@ -64,11 +64,20 @@ impl SmartCache {
         }
     }
 
-    /// Check if should pre-cache queue items
+    /// Check if should pre-cache queue items.
+    ///
+    /// Note this deliberately does NOT consult `wifi_only`. It used to return
+    /// `queue_precache_enabled && !wifi_only`, which disabled precaching
+    /// outright whenever the user enabled WiFi-only — regardless of the network
+    /// actually in use. The network check now lives in the download queue pump
+    /// (`downloads_allowed_on_current_network`), which is the single gate for
+    /// all download traffic, so this only answers "is precaching enabled?".
+    ///
+    /// TRACES: UR-053 | DR-074
     pub fn should_precache_queue(&self) -> bool {
         self.config
             .lock()
-            .map(|cfg| cfg.queue_precache_enabled && !cfg.wifi_only)
+            .map(|cfg| cfg.queue_precache_enabled)
             .unwrap_or(false)
     }
 
@@ -282,6 +291,19 @@ mod tests {
         assert!(cache.should_precache_queue());
     }
 
+    #[test]
+    fn test_wifi_only_does_not_disable_precaching() {
+        // wifi_only must not short-circuit precaching: the network gate lives in
+        // the download pump, which checks the *actual* transport. Enabling
+        // WiFi-only while on WiFi should still precache.
+        let mut config = CacheConfig::default();
+        config.queue_precache_enabled = true;
+        config.wifi_only = true;
+
+        let cache = SmartCache::new(config);
+        assert!(cache.should_precache_queue());
+    }
+
     #[tokio::test]
     async fn test_storage_limit_check() {
         use crate::storage::db_service::RusqliteService;