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

AGENTS.md

@@ -173,6 +173,7 @@ if canonical == "mycommand":
 - `args_hint` — argument placeholder shown in help (e.g. `"<prompt>"`, `"[name]"`)
 - `cli_only` — only available in the interactive CLI
 - `gateway_only` — only available in messaging platforms
+- `gateway_config_gate` — config dotpath (e.g. `"display.tool_progress_command"`); when set on a `cli_only` command, the command becomes available in the gateway if the config value is truthy. `GATEWAY_KNOWN_COMMANDS` always includes config-gated commands so the gateway can dispatch them; help/menus only show them when the gate is open.
 
 **Adding an alias** requires only adding it to the `aliases` tuple on the existing `CommandDef`. No other file changes needed — dispatch, help text, Telegram menu, Slack mapping, and autocomplete all update automatically.