feat(slack): add --no-assistant flag to manifest generation

By default `hermes slack manifest` opts the app into Slack's AI Assistant
container (assistant_view feature + assistant:write scope +
assistant_thread_* events). Slack then renders DMs as the right-hand
Assistant split-pane, where every exchange is a thread and bare slash
commands (/help, /new, ...) are not delivered as normal command events —
they only work when the bot is @mentioned. There was no way to opt out
short of hand-editing the generated JSON.

Add --no-assistant to emit a flat-DM manifest that omits those three
pieces, so DMs render as a normal chat and slash commands dispatch
inline. The regular messaging surface (Messages tab, slash commands,
Socket Mode, channel + DM scopes/events) is preserved in both modes.

Default behaviour is unchanged (assistant mode still on).

Tests: cover both manifest modes and the argparse wiring.

tests/hermes_cli/test_slack_cli.py

@@ -1,6 +1,30 @@
 """Tests for Slack CLI helpers."""
 
+import argparse
+
 from hermes_cli.slack_cli import _build_full_manifest
+from hermes_cli.subcommands.slack import build_slack_parser
+
+
+def _parse_slack_args(argv):
+    """Build the real `hermes slack` parser and parse argv against it."""
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers(dest="command")
+    build_slack_parser(subparsers, cmd_slack=lambda _args: 0)
+    return parser.parse_args(argv)
+
+
+class TestSlackManifestArgparse:
+    """The `--no-assistant` flag wires through argparse to `no_assistant`."""
+
+    def test_no_assistant_flag_defaults_false(self):
+        args = _parse_slack_args(["slack", "manifest"])
+        assert getattr(args, "no_assistant", False) is False
+
+    def test_no_assistant_flag_sets_true(self):
+        args = _parse_slack_args(["slack", "manifest", "--no-assistant"])
+        assert args.no_assistant is True
+
 
 
 class TestSlackFullManifest:
@@ -28,3 +52,35 @@ class TestSlackFullManifest:
         assert "assistant:write" in manifest["oauth_config"]["scopes"]["bot"]
         bot_events = manifest["settings"]["event_subscriptions"]["bot_events"]
         assert "assistant_thread_started" in bot_events
+
+    def test_no_assistant_omits_assistant_pieces(self):
+        manifest = _build_full_manifest(
+            "Hermes", "Your Hermes agent on Slack", include_assistant=False
+        )
+
+        # assistant_view feature is gone -> Slack renders a flat DM, not the
+        # Assistant thread pane (where bare slash commands don't dispatch).
+        assert "assistant_view" not in manifest["features"]
+        assert "assistant:write" not in manifest["oauth_config"]["scopes"]["bot"]
+        bot_events = manifest["settings"]["event_subscriptions"]["bot_events"]
+        assert "assistant_thread_started" not in bot_events
+        assert "assistant_thread_context_changed" not in bot_events
+
+    def test_no_assistant_preserves_core_surface(self):
+        """Dropping assistant mode must NOT strip the regular messaging surface."""
+        manifest = _build_full_manifest(
+            "Hermes", "Your Hermes agent on Slack", include_assistant=False
+        )
+
+        # Flat DM still needs the Messages tab writable.
+        assert manifest["features"]["app_home"]["messages_tab_enabled"] is True
+        # Slash commands and Socket Mode are independent of assistant mode.
+        assert manifest["features"]["slash_commands"]
+        assert manifest["settings"]["socket_mode_enabled"] is True
+        # Channel + DM scopes/events survive so the bot still works everywhere.
+        bot_scopes = manifest["oauth_config"]["scopes"]["bot"]
+        for scope in ("commands", "channels:history", "groups:read", "im:history"):
+            assert scope in bot_scopes
+        bot_events = manifest["settings"]["event_subscriptions"]["bot_events"]
+        for event in ("message.im", "message.channels", "message.groups", "app_mention"):
+            assert event in bot_events