tests: add functionnal tests (e2e if you will)

tests/functional/README.md

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+# Functional Tests
+
+End-to-end tests that make real API calls to a Codeberg instance.
+
+## Running Tests
+
+These tests require special setup and credentials. See [SETUP_FUNCTIONAL_TESTS.md](../../SETUP_FUNCTIONAL_TESTS.md) for complete instructions.
+
+### Quick Start
+
+```bash
+export CODEBERG_TEST_TOKEN="your_token"
+export CODEBERG_TEST_OWNER="test-account-username"
+export CODEBERG_TEST_REPO="test-repo-name"
+
+go test -v -race -tags=functional ./...
+```
+
+### What They Test
+
+- ✅ API authentication and connectivity
+- ✅ Repository listing and details
+- ✅ Issue creation, listing, retrieval
+- ✅ Issue comments
+- ✅ API error handling
+- ✅ Repository secrets and actions (if available)
+
+### CI Integration
+
+These tests run automatically in CI when configured:
+- Only on `main` branch and pull requests
+- Requires `CODEBERG_TEST_TOKEN` secret and configuration variables
+- Uses a dedicated test account (not your personal account)
+
+### Files
+
+- `functional_test.go` - Test suite with all test cases
+- `fixtures.go` - Helper functions and test environment setup