Refactor everything that's used all over into a common/ package and sync files from static/ into public/ so that public's not in the git.

common/errors.go

@@ -0,0 +1,12 @@
+package common
+
+import (
+  "log"
+  "fmt"
+)
+
+func Fail(err error, format string, v ...any) error {
+  err_format := fmt.Sprintf("ERROR: %v; %s", err, format)
+  log.Printf(err_format, v...)
+  return err
+}