Add unit tests, integration test, CI workflow, and conventions

- gitea/client_test.go: mock HTTP tests for all API methods + error cases
- llm/client_test.go: mock tests for completion, errors, timeouts
- review/parser_test.go: JSON parsing, markdown fences, validation
- review/formatter_test.go: markdown output, empty/multiple findings
- review/prompt_test.go: system/user prompt construction
- integration_test.go: full end-to-end flow (build tag: integration)
- .gitea/workflows/ci.yml: test + vet + build on push, dual LLM review on PRs
- CONVENTIONS.md: coding standards for self-review dogfooding
- README.md: usage docs, env vars, architecture

CONVENTIONS.md

@@ -0,0 +1,32 @@
+# Conventions
+
+## Language & Dependencies
+
+- Go standard library only — no external dependencies.
+- Target the latest stable Go release.
+
+## Error Handling
+
+- Return errors; never panic.
+- Wrap errors with context using `fmt.Errorf("context: %w", err)`.
+- Check all error returns.
+
+## Testing
+
+- Test every exported function.
+- Use `net/http/httptest` for HTTP mocking.
+- Table-driven tests where multiple inputs share the same assertion logic.
+- Integration tests use build tags (`//go:build integration`).
+
+## Style
+
+- Keep functions short and focused.
+- Prefer early returns over deep nesting.
+- Meaningful variable names — no single-letter names outside loop indices.
+- Comments explain *why*, not *what*.
+
+## Process
+
+- `go test ./...` must pass before commit.
+- `go vet ./...` must pass before commit.
+- Keep commits atomic and well-described.