docs: add missing pages to sidebar navigation (#10758)

* feat: implement register_command() on plugin context

Complete the half-built plugin slash command system. The dispatch
code in cli.py and gateway/run.py already called
get_plugin_command_handler() but the registration side was never
implemented.

Changes:
- Add register_command() to PluginContext — stores handler,
  description, and plugin name; normalizes names; rejects conflicts
  with built-in commands
- Add _plugin_commands dict to PluginManager
- Add commands_registered tracking on LoadedPlugin
- Add get_plugin_command_handler() and get_plugin_commands()
  module-level convenience functions
- Fix commands.py to use actual plugin description in Telegram
  bot menu (was hardcoded 'Plugin command')
- Add plugin commands to SlashCommandCompleter autocomplete
- Show command count in /plugins display
- 12 new tests covering registration, conflict detection,
  normalization, handler dispatch, and introspection

Closes #10495

* docs: add register_command() to plugin guides

- Build a Plugin guide: new 'Register slash commands' section with
  full API reference, comparison table vs register_cli_command(),
  sync/async examples, and conflict protection docs
- Features/Plugins page: add slash commands to capabilities table
  and plugin types summary

* docs: add missing pages to sidebar navigation

- guides/aws-bedrock → Guides & Tutorials
- user-guide/features/credential-pools → Integrations

website/sidebars.ts

@@ -137,6 +137,7 @@ const sidebars: SidebarsConfig = {
         'user-guide/features/honcho',
         'user-guide/features/provider-routing',
         'user-guide/features/fallback-providers',
+        'user-guide/features/credential-pools',
       ],
     },
     {
@@ -159,6 +160,7 @@ const sidebars: SidebarsConfig = {
         'guides/work-with-skills',
         'guides/delegation-patterns',
         'guides/migrate-from-openclaw',
+        'guides/aws-bedrock',
       ],
     },
     {