build: enable R8 minification and fix release lint namespace typos

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

app/proguard-rules.pro

@@ -0,0 +1,11 @@
+# R8/ProGuard rules for resbuilder_app.
+
+# Gson reflects over the API data models. Keep their fields intact.
+-keep class com.example.resbuilder.data.model.** { <fields>; }
+
+# Keep the OkHttp client class and its members (OkHttp ships its own consumer rules,
+# but ApiClient is referenced reflectively nowhere; keep it to be safe).
+-keep class com.example.resbuilder.data.remote.ApiClient { *; }
+
+# Credential Manager / Google Identity libs register via reflection.
+-keep class com.google.android.libraries.identity.googleid.** { *; }

app/src/main/res/drawable/bg_banner_warning.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk"
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
     android:shape="rectangle">
     <solid android:color="?attr/colorWarningContainer" />
     <corners android:radius="12dp" />

app/src/main/res/drawable/bg_status_badge.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk/android"
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
     android:shape="rectangle">
     <solid android:color="?attr/colorSurfaceContainerHighest" />
     <corners android:radius="8dp" />

app/src/main/res/layout/activity_admin.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/android"
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"

app/src/main/res/layout/fragment_result.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/android"
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"

app/src/main/res/layout/item_admin_user.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<com.google.android.material.card.MaterialCardView xmlns:android="http://schemas.android.com/apk/android"
+<com.google.android.material.card.MaterialCardView xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"