shell: return flag parse errors from every command (#12618)

* shell: return flag parse errors from every command

48 commands returned nil when their flags failed to parse, so a mistyped
flag printed the flag error but the command still counted as a success:
a piped weed shell run exited 0, the master maintenance loop logged no
error, and admin script jobs reported the line as done.

Return the parse error as s3.bucket.create (#12544) and the other shell
commands already do. TestCommandsReturnFlagParseErrors runs every
registered command with an unknown flag and fails for the 48 on master.

Signed-off-by: anant <170962632+antcybersec@users.noreply.github.com>

* shell: don't report -h as a failure

With the parse errors returned, -h on those commands now returns
flag.ErrHelp, so the shell printed "error: flag: help requested" and a
piped run exited 1. The flag package has already printed the usage, so
processEachCmd now treats flag.ErrHelp as success for every command.

Signed-off-by: anant <170962632+antcybersec@users.noreply.github.com>

* shell: keep the -h test beside the flag parse test

TestProcessEachCmdTreatsHelpAsSuccess covers the same change as
TestCommandsReturnFlagParseErrors, so it lives in the same new file and
shell_liner_test.go stays as it was.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Signed-off-by: anant <170962632+antcybersec@users.noreply.github.com>
Co-authored-by: anant <170962632+antcybersec@users.noreply.github.com>
Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/shell/command_ec_encode.go

@@ -114,7 +114,7 @@ func (c *commandEcEncode) Do(args []string, commandEnv *CommandEnv, writer io.Wr
 	verbose := encodeCommand.Bool("verbose", false, "show detailed reasons why volumes are not selected for encoding")
 
 	if err = encodeCommand.Parse(args); err != nil {
-		return nil
+		return err
 	}
 	if err = commandEnv.confirmIsLocked(args); err != nil {
 		return