Shell completion was broken for all subcommands. Typing `aicr bundle --<TAB>`
executed the command instead of showing flag completions because a custom
`commandLister` on the root command overrode urfave/cli's built-in completion
and only listed top-level subcommand names — never flags.

Three issues are fixed:

1. Remove `commandLister` and replace it with `completeWithAllFlags`, a custom
   ShellComplete function that lists all flag names including aliases (e.g.
   both `--accelerator` and `--gpu`). The function is applied recursively to
   all subcommands via `setShellComplete` so urfave/cli's `setupDefaults`
   cannot replace it with `DefaultCompleteWithFlags` (which omits aliases).

2. Work around a urfave/cli v3 bug where `--` immediately before
   `--generate-shell-completion` disables completion mode entirely
   (`checkShellCompleteFlag` treats `--` as a POSIX flag terminator). This
   caused `aicr snapshot --<TAB>` to execute the snapshot action — deploying
   an agent to the cluster. `sanitizeCompletionArgs` replaces the bare `--`
   with `-` before passing args to `cmd.Run`, keeping completion mode active.

3. Read `os.Args` directly (via `completionLastArg`) instead of `cmd.Args()`
   to determine what the user was typing. Partial flags like `--form` fail
   urfave/cli's flag parser and never appear in parsed positional args, so
   `cmd.Args()` is empty. `os.Args` always has the original command line.

Also removes `EnableShellCompletion: true` from 7 subcommands — the field is
only meaningful on the root command in urfave/cli v3.