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

.github/workflows/ci.yml

@@ -0,0 +1,51 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+    branches: [ main, master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: [1.21.x, 1.22.x]
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: ${{ matrix.go-version }}
+
+    - name: Download dependencies
+      run: go mod download
+
+    - name: Build
+      run: go build -v ./...
+
+    - name: Test
+      run: go test -v -race ./...
+
+    - name: Lint
+      run: |
+        go vet ./...
+        test -z $(gofmt -l .)
+
+  security-scan:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: 1.21.x
+
+    - name: Run GoSec
+      uses: securego/gosec@v2
+      with:
+        args: ./...