Record file mode in the manifest, 0000 unless asked (closes #161)

MFFilePath gains mode (field 304): a file's permission bits, 0777 at
most, or 0000, meaning none recorded. gen and freshen record real modes
only with --include-permissions (ScannerOptions.IncludePermissions); the
builder keeps only mode.Perm(), so setuid, setgid and sticky are never
written. list -l and export show the mode in octal. check reports
MODE_MISMATCH for a recorded mode other than 0000 the file lacks. fetch
refuses a manifest with a mode above 0777 before requesting any file,
sets only the permission bits of each recorded mode on the files it
writes, and downloads again a present file whose mode differs. The decoding-cost bound counts a file
entry at 176 bytes, up from 160.

Model: opus-5-5

internal/cli/list.go

@@ -52,8 +52,8 @@ func (mfa *CLIApp) listManifestOperation(ctx context.Context, cmd *cli.Command)
 				mtimeStr = mtime.Format(time.RFC3339)
 			}
 
-			_, _ = fmt.Fprintf(mfa.Stdout, "%d\t%s\t%s%s",
-				f.GetSize(), mtimeStr, f.GetPath(), lineEnd)
+			_, _ = fmt.Fprintf(mfa.Stdout, "%04o\t%d\t%s\t%s%s",
+				f.GetMode(), f.GetSize(), mtimeStr, f.GetPath(), lineEnd)
 		} else {
 			_, _ = fmt.Fprintf(mfa.Stdout, "%s%s", f.GetPath(), lineEnd)
 		}