Add Makefile with check, lint, test, fmt targets

- check: default target, runs fmt-check, lint, and test
- fmt-check: verifies code is properly formatted
- fmt: formats code with gofmt
- lint: runs golangci-lint
- test: runs go test
- build: builds pixad binary with version info
- clean: removes build artifacts

TODO.md

@@ -3,7 +3,7 @@
 A single linear checklist of tasks to implement the complete pixa caching image reverse proxy server.
 
 ## Project Setup
-- [ ] Create Makefile with check, lint, test, fmt targets
+- [x] Create Makefile with check, lint, test, fmt targets
 - [ ] Create project structure (cmd/pixad, internal/*)
 - [ ] Implement globals package
 - [ ] Implement logger package