refactor(app): provide sub-config structures from main config

Extract DatabaseConfig, RedisConfig, RustFSConfig, LogConfig, and EmailConfig
from the main Config to enable pkg/* package constructors to receive specific
config types by value, supporting the fx.Lifecycle OnStop hooks pattern.

cmd/genhash/main.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"carrotskin/pkg/auth"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Fprintln(os.Stderr, "usage: genhash <password>")
+		os.Exit(2)
+	}
+	h, err := auth.HashPassword(os.Args[1])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "err:", err)
+		os.Exit(1)
+	}
+	fmt.Print(h)
+}