feat: config-gated /verbose command for messaging gateway (#3262)

* feat: config-gated /verbose command for messaging gateway

Add gateway_config_gate field to CommandDef, allowing cli_only commands
to be conditionally available in the gateway based on a config value.

- CommandDef gains gateway_config_gate: str | None — a config dotpath
  that, when truthy, overrides cli_only for gateway surfaces
- /verbose uses gateway_config_gate='display.tool_progress_command'
- Default is off (cli_only behavior preserved)
- When enabled, /verbose cycles tool_progress mode (off/new/all/verbose)
  in the gateway, saving to config.yaml — same cycle as the CLI
- Gateway helpers (help, telegram menus, slack mapping) dynamically
  check config to include/exclude config-gated commands
- GATEWAY_KNOWN_COMMANDS always includes config-gated commands so
  the gateway recognizes them and can respond appropriately
- Handles YAML 1.1 bool coercion (bare 'off' parses as False)
- 8 new tests for the config gate mechanism + gateway handler

* docs: document gateway_config_gate and /verbose messaging support

- AGENTS.md: add gateway_config_gate to CommandDef fields
- slash-commands.md: note /verbose can be enabled for messaging, update Notes
- configuration.md: add tool_progress_command to display section + usage note
- cli.md: cross-link to config docs for messaging enablement
- messaging/index.md: show tool_progress_command in config snippet
- plugins.md: add gateway_config_gate to register_command parameter table

website/docs/user-guide/features/plugins.md

@@ -83,6 +83,7 @@ The handler receives the argument string (everything after `/greet`) and returns
 | `aliases` | Tuple of alternative names |
 | `cli_only` | Only available in CLI |
 | `gateway_only` | Only available in messaging platforms |
+| `gateway_config_gate` | Config dotpath (e.g. `"display.my_option"`). When set on a `cli_only` command, the command becomes available in the gateway if the config value is truthy. |
 
 ## Managing plugins