FRE-680: Initial project scaffold with auth & API client

- Set up Go module with Cobra CLI skeleton
- Implemented login/logout/session commands with 2FA support
- Created ProtonMail API client with rate limiting
- Added config management for ~/.config/pop/
- Configured CI/CD pipeline with GitHub Actions
- Added Makefile for build/test/lint targets

Files:
- main.go, go.mod, go.sum
- cmd/root.go, cmd/auth.go
- internal/auth/session.go
- internal/config/config.go
- internal/api/client.go
- Makefile, README.md, .gitignore
- .github/workflows/ci.yml

README.md

@@ -0,0 +1,115 @@
+# pop
+
+A ProtonMail CLI tool written in Go, similar to gog.
+
+## Features
+
+- **Authentication**: Login/logout with 2FA support
+- **Session Management**: Secure token storage in `~/.config/pop/`
+- **ProtonMail API Client**: REST client with rate limiting and error handling
+- **PGP Encryption**: Full support for ProtonMail's PGP encryption via gopenpgp v2
+
+## Installation
+
+```bash
+# Build from source
+git clone https://github.com/frenocorp/pop.git
+cd pop
+make build
+
+# Install
+make install
+```
+
+## Usage
+
+```bash
+# Initialize login (interactive mode)
+pop login
+
+# Login with explicit credentials
+pop login --email user@proton.me --password secret
+
+# Check current session
+pop session
+
+# Logout
+pop logout
+```
+
+## Project Structure
+
+```
+pop/
+├── cmd/
+│   ├── root.go       # CLI root command
+│   └── auth.go       # Authentication commands
+├── internal/
+│   ├── auth/         # Session management
+│   │   └── session.go
+│   ├── config/       # Configuration handling
+│   │   └── config.go
+│   └── api/          # ProtonMail API client
+│       └── client.go
+├── .github/
+│   └── workflows/
+│       └── ci.yml    # CI/CD pipeline
+├── go.mod
+├── go.sum
+├── main.go
+├── Makefile
+└── README.md
+```
+
+## Configuration
+
+Configuration is stored in `~/.config/pop/config.json`:
+
+```json
+{
+  "api_base_url": "https://api.protonmail.ch",
+  "timeout_sec": 30,
+  "rate_limit_requests": 100,
+  "rate_limit_window_sec": 60
+}
+```
+
+Session data is stored in `~/.config/pop/session.json`:
+
+```json
+{
+  "uid": "user-uid",
+  "access_token": "token",
+  "refresh_token": "refresh",
+  "expires_at": 0,
+  "two_factor_enabled": false
+}
+```
+
+## Development
+
+```bash
+# Build
+make build
+
+# Run tests
+make test
+
+# Format code
+make fmt
+
+# Lint
+make lint
+
+# Clean build artifacts
+make clean
+```
+
+## Dependencies
+
+- [github.com/spf13/cobra](https://github.com/spf13/cobra) - CLI framework
+- [github.com/ProtonMail/gopenpgp/v2](https://github.com/ProtonMail/gopenpgp) - PGP crypto
+
+## License
+
+MIT