feat: Set up Fastlane for Android with Firebase App Distribution and adjust build configurations.

android/fastlane/Appfile

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+json_key_file("'/Users/dayronvanleemput/Documents/Coding/clé/travelmate-a47f5-1e4759031f2d.json'") # Path to the json secret file - Follow https://docs.fastlane.tools/actions/supply/#setup to get one
+package_name("be.devdayronvl.travel_mate") # e.g. com.krausefx.app

android/fastlane/Fastfile

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+default_platform(:android)
+
+platform :android do
+  desc "Déploiement Firebase via Gitea"
+  lane :deploy_firebase do
+    # 1. Décoder le Keystore depuis les secrets Gitea (voir Phase 4)
+    # On vérifie si le fichier existe déjà pour éviter d'écraser en local
+    if ENV['ANDROID_KEYSTORE_BASE64']
+      File.open("upload-keystore.jks", "wb") do |f|
+        f.write(Base64.decode64(ENV['ANDROID_KEYSTORE_BASE64']))
+      end
+    end
+
+    # 2. Construire l'APK
+    flutter_build(build: "apk") 
+    # Note: Fastlane a un plugin flutter, ou utilisez sh("flutter build apk --release")
+
+    # 3. Envoyer à Firebase
+    firebase_app_distribution(
+      app: ENV["FIREBASE_ANDROID_APP_ID"],
+      service_credentials_file: "firebase_credentials.json",
+      groups: "testers",
+      release_notes: "Build automatique depuis Gitea Commit: #{ENV['GITHUB_SHA']}"
+    )
+  end
+end

android/fastlane/Pluginfile

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+# Autogenerated by fastlane
+#
+# Ensure this file is checked in to source control!
+
+gem 'fastlane-plugin-firebase_app_distribution'