Tool: Polish Pass 1

In sow-tools, extract now behaves like a real sync by default: it
overwrites changed extracted files, removes stale extracted files that
no longer exist in the built archives, and normalizes extracted resource
filenames to lowercase. I also made validation warn on uppercase
resource filenames so mixed-case names like I_ELVENCHAIN are surfaced
instead of quietly lingering. The extract command output now includes
overwritten and removed counts too.

internal/app/app.go

@@ -181,6 +181,8 @@ func runExtract(ctx context) error {
 		fmt.Fprintf(ctx.stdout, "hak archives: %d\n", len(result.HAKPaths))
 	}
 	fmt.Fprintf(ctx.stdout, "written: %d\n", result.Written)
+	fmt.Fprintf(ctx.stdout, "overwritten: %d\n", result.Overwritten)
+	fmt.Fprintf(ctx.stdout, "removed: %d\n", result.Removed)
 	fmt.Fprintf(ctx.stdout, "skipped: %d\n", result.Skipped)
 	return nil
 }