feat(help): show version, command counts, and allowed/disabled builtins

[julesmcrt]

Summary

Depends on #183 (version package and release workflow). Target that PR first.

• The help builtin now shows a header with the rshell version and builtin count
• When commands are restricted, help shows a compact "Disabled builtins:" list and help --all shows both sections as full description tables
• When all builtins are allowed and --all is used, shows "All builtins are allowed in this session."

Before / After

1. ./rshell --allowed-commands "rshell:echo,rshell:help,rshell:ls" -c 'help'

Only 3 builtins are allowed. Running help without --all.

Before:

echo  write arguments to stdout
help  display help for commands
ls    list directory contents

Run 'help <command>' for more information on a specific command.

After:

rshell 0.0.10 — 3 of 28 builtins enabled

echo  write arguments to stdout
help  display help for commands
ls    list directory contents

Disabled builtins: [, break, cat, continue, cut, exit, false, find, grep, head, ip, ping,
  printf, ps, sed, sort, ss, strings, tail, test, tr, true, uname, uniq, wc

Run 'help <command>' for more information on a specific command.

2. ./rshell --allowed-commands "rshell:echo,rshell:help,rshell:ls" -c 'help --all'

Only 3 builtins are allowed. Running help --all to see full descriptions for disabled builtins too.

Before:

help: unknown flag: --all

After:

rshell 0.0.10 — 3 of 28 builtins enabled

echo  write arguments to stdout
help  display help for commands
ls    list directory contents

Disabled builtins:
[         evaluate conditional expression
break     exit from a loop
cat       concatenate and print files
continue  continue a loop iteration
cut       remove sections from each line
exit      exit the shell
false     return unsuccessful exit status
find      search for files in a directory hierarchy
grep      print lines that match patterns
head      output the first part of files
ip        show network interface and routing information
ping      send ICMP echo requests to a network host
printf    format and print data
ps        report process status
sed       stream editor for filtering and transforming text
sort      sort lines of text files
ss        display socket statistics
strings   print printable character sequences
tail      output the last part of files
test      evaluate conditional expression
tr        translate or delete characters
true      return successful exit status
uname     print system information
uniq      report or omit repeated lines
wc        print newline, word, and byte counts

Run 'help <command>' for more information on a specific command.

3. ./rshell --allow-all-commands -c 'help'

All builtins are allowed. Running help without --all.

Before:

[         evaluate conditional expression
break     exit from a loop
...
wc        print newline, word, and byte counts

Run 'help <command>' for more information on a specific command.

After:

rshell 0.0.10 — All 28 builtins available

[         evaluate conditional expression
break     exit from a loop
...
wc        print newline, word, and byte counts

Run 'help <command>' for more information on a specific command.

4. ./rshell --allow-all-commands -c 'help --all'

All builtins are allowed. Running help --all.

Before:

help: unknown flag: --all

After:

rshell 0.0.10 — All 28 builtins available

[         evaluate conditional expression
...
wc        print newline, word, and byte counts

All builtins are allowed in this session.

Run 'help <command>' for more information on a specific command.

Test plan

• All existing help tests updated and passing
• New tests for header, --all flag, restricted "Disabled builtins:" output
• Scenario tests assert full stdout (not just stdout_contains)
• Full test suite passes (go test ./... — 43 packages, 0 failures)
• Symbol analysis tests pass (new internal/version.Version added to allowlists)

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