Refactor Gemini protocol implementation and improve server architecture

- Move gemini URL parsing from common/ to gemini/ package
- Add structured status codes in gemini/status_codes.go
- Improve error handling with proper Gemini status codes
- Update configuration field naming (Listen -> ListenAddr)
- Add UTF-8 validation for URLs
- Enhance security with better path validation
- Add CLAUDE.md for development guidance
- Include example content in srv/ directory
- Update build system to use standard shell

go.mod

@@ -2,12 +2,20 @@ module gemserve
 
 go 1.24.3
 
+toolchain go1.24.4
+
 require (
 	git.antanst.com/antanst/logging v0.0.1
-	git.antanst.com/antanst/xerrors v0.0.1
 	git.antanst.com/antanst/uid v0.0.1
+	git.antanst.com/antanst/xerrors v0.0.1
 	github.com/gabriel-vasile/mimetype v1.4.8
 	github.com/matoous/go-nanoid/v2 v2.1.0
 )
 
 require golang.org/x/net v0.33.0 // indirect
+
+replace git.antanst.com/antanst/xerrors => ../xerrors
+
+replace git.antanst.com/antanst/uid => ../uid
+
+replace git.antanst.com/antanst/logging => ../logging