Implement pure Go Git HTTP server without CLI dependencies

Major rewrite to eliminate git CLI dependency:
- Created object package for Git object format handling (blob, tree, commit)
- Implemented packfile generation from scratch
- Rewrote repo initialization to create Git repos without CLI
- Implemented git-upload-pack protocol in pure Go
- Updated all server handlers to use new implementation
- Added Git packet tracing to test.sh for debugging
- Fixed tests to work with new implementation

The server now works entirely with Go code, no git commands needed.
Clone operations work correctly, but pull operations still have protocol
negotiation issues that need further debugging.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

go.mod

@@ -6,6 +6,7 @@ require (
 	dario.cat/mergo v1.0.0 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/ProtonMail/go-crypto v1.1.6 // indirect
+	github.com/chainguard-dev/clog v1.7.0 // indirect
 	github.com/cloudflare/circl v1.6.1 // indirect
 	github.com/cyphar/filepath-securejoin v0.4.1 // indirect
 	github.com/emirpasic/gods v1.18.1 // indirect
@@ -17,6 +18,7 @@ require (
 	github.com/kevinburke/ssh_config v1.2.0 // indirect
 	github.com/pjbgf/sha1cd v0.3.2 // indirect
 	github.com/sergi/go-diff v1.3.2-0.20230802210424-5b0b94c5c0d3 // indirect
+	github.com/sethvargo/go-envconfig v1.3.0 // indirect
 	github.com/skeema/knownhosts v1.3.1 // indirect
 	github.com/xanzy/ssh-agent v0.3.3 // indirect
 	golang.org/x/crypto v0.37.0 // indirect