feat: WiFi-only download mode

- Add network mode setting (any/wifi_only) in settings model
- Add connectivity check in download queue processor
- Downloads pause automatically when on mobile data (if wifi_only enabled)
- Add UI toggle in Download Settings page
- Add localization strings for network mode setting
- Bump version to 3.3.6+71

pubspec.lock

@@ -185,6 +185,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.19.1"
+  connectivity_plus:
+    dependency: "direct main"
+    description:
+      name: connectivity_plus
+      sha256: b5e72753cf63becce2c61fd04dfe0f1c430cc5278b53a1342dc5ad839eab29ec
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.1.5"
+  connectivity_plus_platform_interface:
+    dependency: transitive
+    description:
+      name: connectivity_plus_platform_interface
+      sha256: "42657c1715d48b167930d5f34d00222ac100475f73d10162ddf43e714932f204"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.1"
   convert:
     dependency: transitive
     description:
@@ -637,6 +653,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "5.6.1"
+  nm:
+    dependency: transitive
+    description:
+      name: nm
+      sha256: "2c9aae4127bdc8993206464fcc063611e0e36e72018696cd9631023a31b24254"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.5.0"
   node_preamble:
     dependency: transitive
     description: