feat: implement Android app signing setup and update .gitignore for keystore files

android/SIGNING_SETUP.md

@@ -0,0 +1,61 @@
+# Android App Signing Setup
+
+## Why This Matters
+Android requires apps to be signed with the same key for updates to work. Without proper signing, users cannot update your app - they must uninstall and reinstall, losing all data.
+
+## Setup Instructions
+
+### 1. Create a Keystore (if you don't have one)
+
+Run this command in the `android/` directory:
+
+```bash
+keytool -genkey -v -keystore paarrot-release.keystore -alias paarrot -keyalg RSA -keysize 2048 -validity 10000
+```
+
+You'll be asked for:
+- Keystore password (remember this!)
+- Key password (remember this!)  
+- Your name, organization, etc.
+
+**IMPORTANT**: Back up this keystore file and remember the passwords! If you lose either, you cannot update your app.
+
+### 2. Create keystore.properties
+
+Copy the example file:
+
+```bash
+cp keystore.properties.example keystore.properties
+```
+
+Then edit `keystore.properties` and fill in:
+- `storeFile`: path to your keystore (e.g., `paarrot-release.keystore`)
+- `storePassword`: the keystore password you set
+- `keyAlias`: the alias (e.g., `paarrot`)
+- `keyPassword`: the key password you set
+
+### 3. Verify
+
+The file `keystore.properties` should be gitignored (check `.gitignore`).
+
+### 4. Build
+
+Now your release builds will be properly signed:
+
+```bash
+cd android
+./gradlew assembleRelease
+```
+
+The signed APK will be in: `app/build/outputs/apk/release/`
+
+## Troubleshooting
+
+### "Updates not installing"
+- You're using a different keystore than the original APK
+- Solution: Use the same keystore that was used for the first release
+
+### "keystore.properties not found"
+- Normal for debug builds
+- Only needed for release builds
+- Create the file following step 2 above