feat: add Play Store publish workflow and signing config

PUBLISHING.md

@@ -0,0 +1,54 @@
+# Publishing to Google Play Store
+
+## Required GitHub Secrets
+
+Configure these in **Settings > Secrets and variables > Actions**:
+
+| Secret | Description |
+|--------|-------------|
+| `PLAY_STORE_SERVICE_ACCOUNT_JSON` | Google Play Console service account JSON key (full JSON content) |
+| `KEYSTORE_BASE64` | Base64-encoded release keystore (`base64 -w0 release.keystore`) |
+| `KEYSTORE_PASSWORD` | Keystore password |
+| `KEY_ALIAS` | Key alias in the keystore |
+| `KEY_PASSWORD` | Key password |
+
+## Setup Steps
+
+### 1. Create a release keystore
+
+```bash
+keytool -genkeypair -v -storetype PKCS12 \
+  -keystore release.keystore -alias release \
+  -keyalg RSA -keysize 2048 -validity 10000
+```
+
+Encode it for GitHub secrets:
+```bash
+base64 -w0 release.keystore
+```
+
+### 2. Create a Google Play service account
+
+1. Go to [Google Cloud Console](https://console.cloud.google.com/) > IAM > Service Accounts
+2. Create a service account and download the JSON key
+3. In Google Play Console > Settings > API access, link the service account
+4. Grant it release management permissions for your app
+
+### 3. Workflow triggers
+
+The publish workflow runs on:
+- GitHub Release publish events
+- Tag pushes matching `v*`
+
+It builds an AAB (Android App Bundle), signs it with the release keystore, and uploads to the **internal** track. Promote to production via Play Console.
+
+## Fastlane (Alternative)
+
+A Fastlane setup is included for local publishing:
+
+```bash
+bundle install
+bundle exec fastlane android deploy
+```
+
+Set environment variables: `SUPPLY_JSON_KEY`, `RELEASE_STORE_FILE`, `RELEASE_STORE_PASSWORD`, `RELEASE_KEY_ALIAS`, `RELEASE_KEY_PASSWORD`.