refactor(cli): group subcommand handlers under cli/commands/

Move the eleven per-command modules (backend, cleanup, commit, edit,
info, init, list, login, resume, start, supervise) into a new
bot_bottle/cli/commands/ package, leaving the dispatcher (__init__),
entrypoint (__main__), and shared helpers (_common, tui) at the cli
root. Makes the command surface obvious at a glance and separates
handlers from the plumbing that registers them.

Updated the dispatcher's COMMANDS imports to .commands.*, bumped the
moved files' relative-import depths (.._common, .. import tui, sibling
.start unchanged), and repointed test references to
bot_bottle.cli.commands.*. Full unit suite green (2243); CLI dispatch
verified via `python -m bot_bottle.cli --help`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/cli/commands/backend.py

@@ -0,0 +1,46 @@
+"""`backend` CLI command — generic host setup/status across backends.
+
+`./cli.py backend setup    [--backend=NAME]` provisions (or points at how
+to provision) the chosen backend's one-time host prerequisites.
+`./cli.py backend status   [--backend=NAME]` reports readiness.
+`./cli.py backend teardown [--backend=NAME]` undoes setup (uninstall).
+
+All dispatch to the backend's `setup()` / `status()` / `teardown()`
+classmethods, so there are no backend-specific commands — swapping
+backends is just a different `--backend` (or `$BOT_BOTTLE_BACKEND`, or
+the host default).
+"""
+
+from __future__ import annotations
+
+import argparse
+
+from ...backend import get_bottle_backend, known_backend_names
+from .._common import PROG
+
+
+def cmd_backend(args: list[str]) -> int:
+    parser = argparse.ArgumentParser(
+        prog=f"{PROG} backend",
+        description="Set up or check a backend's host prerequisites.",
+    )
+    parser.add_argument(
+        "action",
+        choices=("setup", "status", "teardown"),
+        help="setup: provision/print host prerequisites; status: report "
+             "readiness; teardown: undo setup (uninstall)",
+    )
+    parser.add_argument(
+        "--backend",
+        choices=known_backend_names(),
+        default=None,
+        help="backend to target (default: $BOT_BOTTLE_BACKEND or the host default)",
+    )
+    ns = parser.parse_args(args)
+
+    backend = get_bottle_backend(ns.backend)
+    if ns.action == "setup":
+        return backend.setup()
+    if ns.action == "teardown":
+        return backend.teardown()
+    return backend.status()