Replace /mode [name] with same-named no-argument commands such as /plan. Update the TUI and ACP snapshots, and validate mode names against command syntax.
The master merge (windows-runtime) shifted TuiConfig's source line without
regenerating docs/config-catalog.md, and its Windows stdout pin for
workspace-edit was recorded on master without dsh-mode — the session/new
result lacked the modes advertisement and the command list lacked /mode.
Both lines carry no filesystem paths, so the POSIX pin's bytes are correct
on Windows too; graft them verbatim.
The remaining red CI on this PR head (windows coverage/static LSP failures,
the web-search live e2e) reproduces on master's own HEAD 32ccc405b and is
not a branch regression.
