security: remove keystore and hardcoded signing credentials

- Remove pixel10.keystore from repository
- Move signing passwords to local.properties (gitignored)
- Add *.keystore and *.jks to .gitignore
- build.gradle.kts now reads credentials from local.properties

After pulling, create local.properties with:
  KEYSTORE_FILE=pixel10.keystore
  KEYSTORE_PASSWORD=<your-password>
  KEY_ALIAS=pixel10
  KEY_PASSWORD=<your-password>

.gitignore

@@ -15,3 +15,5 @@ local.properties
 *.bin
 *.task
 *.tflite
+*.keystore
+*.jks

app/build.gradle.kts

@@ -15,15 +15,19 @@ android {
         versionName = "1.8.0"
     }
 
-    val keystoreFile = rootProject.file("pixel10.keystore")
+    val localProps = rootProject.file("local.properties")
+    val props = java.util.Properties().apply {
+        if (localProps.exists()) load(localProps.inputStream())
+    }
+    val keystoreFile = rootProject.file(props.getProperty("KEYSTORE_FILE", "pixel10.keystore"))
 
     signingConfigs {
         create("release") {
-            if (keystoreFile.exists()) {
+            if (keystoreFile.exists() && props.containsKey("KEYSTORE_PASSWORD")) {
                 storeFile = keystoreFile
-                storePassword = "pixel10ai"
-                keyAlias = "pixel10"
-                keyPassword = "pixel10ai"
+                storePassword = props.getProperty("KEYSTORE_PASSWORD")
+                keyAlias = props.getProperty("KEY_ALIAS", "pixel10")
+                keyPassword = props.getProperty("KEY_PASSWORD")
             }
         }
     }