Hot cache entries now store all data needed to serve a cache hit
without any database access:
- OutputHash (for file lookup)
- ContentType (for Content-Type header)
- SizeBytes (for Content-Length header)
Previously hot cache only stored OutputHash, causing empty
Content-Type headers on cached WebP responses.
- 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
