feat: Phase 28.3 — cellular upload relay + Settings tab

- UploadWorker: 40MB chunked upload to yaris.ceaf.dev (SHA256 check,
  /status resume, WorkManager foreground notification, progress)
- ServerApi extended: uploadStatus + uploadChunk endpoints
- CredentialStore: EncryptedSharedPreferences for server URL/device name/API key
- Settings tab: credential entry (server URL, device name, API key)
- Downloads tab: ↑ Upload button per file, upload progress with cancel
- Upload only shown when credentials configured

android/app/build.gradle.kts

@@ -102,8 +102,8 @@ dependencies {
     // Maps — will be used in 28.4
     // implementation(libs.maplibre)
 
-    // Security — will be used in 28.1.3
-    // implementation(libs.security.crypto)
+    // Security
+    implementation(libs.security.crypto)
 
     // Testing
     testImplementation("junit:junit:4.13.2")