Refactor server package: split handlers and routes into separate files

- Move all handler functions to handlers.go
- Move setupRoutes to routes.go
- Clean up server.go to only contain core server logic
- Add missing GetASDetails and GetPrefixDetails to mockStore for tests
- Fix linter errors (magic numbers, unused parameters, blank lines)

internal/database/interface.go

@@ -47,6 +47,10 @@ type Store interface {
 	// IP lookup operations
 	GetASInfoForIP(ip string) (*ASInfo, error)
 
+	// AS and prefix detail operations
+	GetASDetails(asn int) (*ASN, []LiveRoute, error)
+	GetPrefixDetails(prefix string) ([]LiveRoute, error)
+
 	// Lifecycle
 	Close() error
 }