Adds ToolsConfig.ShellDenyGroups (map[string]bool) so operators can toggle
shell deny groups (package_install, env_dump, etc.) from the /config Web UI
without a process restart.
Wiring:
- ExecTool gains globalDenyGroups + SetGlobalShellDenyGroups (defensive copy).
- effectiveDenyGroups merges per-agent context overrides with global, with
per-key agent precedence — multi-tenant invariant preserved.
- setupToolRegistry applies the initial config before any request can arrive.
- subscribeShellDenyGroupsReload (extracted helper for testability) reacts to
bus.TopicConfigChanged and re-applies the new toggles.
Regression coverage the original PR #1005 attempt missed:
- 6 unit tests for the merge / defensive-copy semantics in internal/tools.
- 3 pub/sub dispatch tests in cmd: happy path, wrong event name, wrong
payload type.
