chore: Secrets handling

[michalurbanek]

No description provided.

[Copilot]

Pull request overview

This PR implements comprehensive secrets management for the Flutter template project using age + sops encryption. The changes move sensitive configuration data (API keys, certificates, Firebase config files) from plaintext to encrypted files, with flavor-specific secret management.

Changes:

• Introduced flutter_dotenv package for environment variable management across flavors
• Implemented encrypted secrets storage using age/sops with shell scripts for encryption/decryption
• Migrated hardcoded configuration values to environment variables loaded from .env files
• Reorganized Android keystore structure and added iOS xcconfig files for secret injection

Reviewed changes

Copilot reviewed 60 out of 64 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
pubspec.yaml	Added flutter_dotenv dependency and .env asset files
lib/app/setup/setup_app.dart	Loads environment variables and replaces hardcoded Firebase config
lib/app/configuration/configuration.dart	Simplified configuration to use dotenv instead of flavor-specific classes
extras/secrets/tools/*.sh	Shell scripts for encrypting, decrypting, and managing secrets
extras/secrets/*.enc	Encrypted secret files for different environments and platforms
makefile	Added secretsDecrypt/Encrypt/Clean commands to workflow
android/app/build.gradle	Updated keystore paths and added Flutter target specifications
ios/Flutter/*.xcconfig	New xcconfig files to inject secrets into iOS builds
.github/workflows/*.yml	Updated CI/CD workflows to decrypt secrets before builds
README.md	Added comprehensive documentation for secrets handling

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