Add R8 keep rules and re-enable release minification

The previous commit disabled isMinifyEnabled/isShrinkResources as a crash
workaround (AGP 9 default minification stripped WorkDatabase_Impl's no-arg
constructor). This commit adds the proper fix:

- new android/app/proguard-rules.pro: keeps the no-arg constructor on all
  RoomDatabase subclasses (the gap the Room AAR's own consumer rule misses
  — it keeps the class name but not the reflectively-called constructor),
  plus WorkManager worker/InputMerger rules re-stated from the work-runtime
  AAR in case transitive consumer-rule propagation is incomplete through the
  Flutter plugin wrapper.
- build.gradle.kts: re-enables isMinifyEnabled=true + isShrinkResources=true
  with proguard-android-optimize.txt + proguard-rules.pro.

Verified on the real phone (BL9000): minified release APK launches without
crash, MainActivity foreground, food-bank suggestions and slot chips render
correctly. APK size 52.1 MB (vs 56.9 MB unminified).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SWPUBzE24Ls9i9GMRwXnnn

app/android/app/build.gradle.kts

@@ -33,14 +33,12 @@ android {
             // TODO: Add your own signing config for the release build.
             // Signing with the debug keys for now, so `flutter run --release` works.
             signingConfig = signingConfigs.getByName("debug")
-            // AGP 9 defaults release minification (and resource shrinking,
-            // which requires it) to true. R8 then strips
-            // WorkDatabase_Impl's reflection-only no-arg constructor (no
-            // keep rule covers it), crashing every release launch with
-            // NoSuchMethodException. Disable both until proper
-            // Room/WorkManager keep rules are added.
-            isMinifyEnabled = false
-            isShrinkResources = false
+            isMinifyEnabled = true
+            isShrinkResources = true
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro",
+            )
         }
     }
 }

app/android/app/proguard-rules.pro

@@ -0,0 +1,20 @@
+# Room: keep generated *_Impl classes and their no-arg constructors.
+# The Room AAR ships "-keep class * extends RoomDatabase" but that only
+# protects the class from removal/renaming — R8 still strips the no-arg
+# constructor because it's only ever called via Class.getDeclaredConstructors()
+# (reflection inside RoomDatabase.create()), which R8 cannot trace statically.
+-keep class * extends androidx.room.RoomDatabase { <init>(); }
+-dontwarn androidx.room.paging.**
+-dontwarn androidx.lifecycle.LiveData
+
+# WorkManager: keep worker classes, their two-arg constructors, and the
+# WorkerParameters type passed to them.  Sourced from work-runtime AAR's
+# own proguard.txt — re-stated here so they apply even if transitive
+# consumer-rule propagation through the Flutter plugin wrapper is incomplete.
+-keepnames class * extends androidx.work.ListenableWorker
+-keepclassmembers public class * extends androidx.work.ListenableWorker {
+    public <init>(...);
+}
+-keep class androidx.work.WorkerParameters
+-keepnames class * extends androidx.work.InputMerger
+-keepclassmembers class * extends androidx.work.InputMerger { void <init>(); }