feat(gateway): expose plugin slash commands natively on all platforms + decision-capable command hook

Plugin slash commands now surface as first-class commands in every gateway
enumerator — Discord native slash picker, Telegram BotCommand menu, Slack
/hermes subcommand map — without a separate per-platform plugin API.

The existing 'command:<name>' gateway hook gains a decision protocol via
HookRegistry.emit_collect(): handlers that return a dict with
{'decision': 'deny'|'handled'|'rewrite'|'allow'} can intercept slash
command dispatch before core handling runs, unifying what would otherwise
have been a parallel 'pre_gateway_command' hook surface.

Changes:

- gateway/hooks.py: add HookRegistry.emit_collect() that fires the same
  handler set as emit() but collects non-None return values. Backward
  compatible — fire-and-forget telemetry hooks still work via emit().
- hermes_cli/plugins.py: add optional 'args_hint' param to
  register_command() so plugins can opt into argument-aware native UI
  registration (Discord arg picker, future platforms).
- hermes_cli/commands.py: add _iter_plugin_command_entries() helper and
  merge plugin commands into telegram_bot_commands() and
  slack_subcommand_map(). New is_gateway_known_command() recognizes both
  built-in and plugin commands so the gateway hook fires for either.
- gateway/platforms/discord.py: extract _build_auto_slash_command helper
  from the COMMAND_REGISTRY auto-register loop and reuse it for
  plugin-registered commands. Built-in name conflicts are skipped.
- gateway/run.py: before normal slash dispatch, call emit_collect on
  command:<canonical> and honor deny/handled/rewrite/allow decisions.
  Hook now fires for plugin commands too.
- scripts/release.py: AUTHOR_MAP entry for @Magaav.
- Tests: emit_collect semantics, plugin command surfacing per platform,
  decision protocol (deny/handled/rewrite/allow + non-dict tolerance),
  Discord plugin auto-registration + conflict skipping, is_gateway_known_command.

Salvaged from #14131 (@Magaav). Original PR added a parallel
'pre_gateway_command' hook and a platform-keyed plugin command
registry; this re-implementation reuses the existing 'command:<name>'
hook and treats plugin commands as platform-agnostic so the same
capability reaches Telegram and Slack without new API surface.

Co-authored-by: Magaav <73175452+Magaav@users.noreply.github.com>

hermes_cli/plugins.py

@@ -283,6 +283,7 @@ class PluginContext:
         name: str,
         handler: Callable,
         description: str = "",
+        args_hint: str = "",
     ) -> None:
         """Register a slash command (e.g. ``/lcm``) available in CLI and gateway sessions.
 
@@ -293,6 +294,13 @@ class PluginContext:
         terminal commands), this registers in-session slash commands that users
         invoke during a conversation.
 
+        ``args_hint`` is an optional short string (e.g. ``"<file>"`` or
+        ``"dias:7 formato:json"``) used by gateway adapters to surface the
+        command with an argument field — for example Discord's native slash
+        command picker. Plugin commands without ``args_hint`` register as
+        parameterless in Discord and still accept trailing text when invoked
+        as free-form chat.
+
         Names conflicting with built-in commands are rejected with a warning.
         """
         clean = name.lower().strip().lstrip("/").replace(" ", "-")
@@ -320,6 +328,7 @@ class PluginContext:
             "handler": handler,
             "description": description or "Plugin command",
             "plugin": self.manifest.name,
+            "args_hint": (args_hint or "").strip(),
         }
         logger.debug("Plugin %s registered command: /%s", self.manifest.name, clean)