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

config/config.go

@@ -14,7 +14,7 @@ type Config struct {
 	ResponseTimeout    int        // Timeout for responses in seconds
 	RootPath           string     // Path to serve files from
 	DirIndexingEnabled bool       // Allow client to browse directories or not
-	Listen             string     // Address to listen on
+	ListenAddr         string     // Address to listen on
 }
 
 var CONFIG Config //nolint:gochecknoglobals
@@ -64,6 +64,6 @@ func GetConfig() *Config {
 		ResponseTimeout:    *responseTimeout,
 		RootPath:           *rootPath,
 		DirIndexingEnabled: *dirIndexing,
-		Listen:             *listen,
+		ListenAddr:         *listen,
 	}
 }