Add optional Nanobot plugin controls (#4396)

* feat: add optional nanobot features

* test: update azure install hint expectation

* fix: validate optional feature extras

maintainer edit: verify requested dependency extras before treating optional features as installed, propagate restart state from feature enablement, and align docs with the new plugins enable command.

* fix: bound optional feature installs

maintainer edit: make optional feature installs time out as a normal install failure instead of leaving the WebUI or CLI action waiting indefinitely.

* feat: slim optional channel dependencies

* fix: log optional install commands

* fix(webui): gate remote feature installs

* docs: clarify webhook plugin example

* fix(webui): harden optional feature installs

* fix: install optional deps without package fallback

* fix(cli): refine plugin feature controls

* fix(webui): count enabled nanobot features

* fix(webui): allow slow feature install routes

* fix(webui): allow disabling websocket channel

* fix(plugins): simplify optional feature controls

* fix(webui): polish apps catalog states

* fix(webui): confirm nanobot support installs

* fix(webui): polish nanobot install dialog

* fix(webui): suppress empty websocket handshakes

* fix(webui): clarify apps plugin summary

* fix(webui): localize workspace access copy

* fix(plugins): polish optional feature controls (#4691)

---------

Co-authored-by: Xubin Ren <52506698+Re-bin@users.noreply.github.com>

nanobot/channels/registry.py

@@ -11,6 +11,7 @@ if TYPE_CHECKING:
     from nanobot.channels.base import BaseChannel
 
 _INTERNAL = frozenset({"base", "manager", "registry"})
+DEFAULT_ENABLED_CHANNELS = frozenset({"websocket"})
 
 
 def discover_channel_names() -> list[str]:
@@ -57,6 +58,7 @@ def discover_enabled(
     *,
     _names: list[str] | None = None,
     _include_all_external: bool = False,
+    warn_import_errors: bool = False,
 ) -> dict[str, type[BaseChannel]]:
     """Return channels whose module names are in *enabled_names*.
 
@@ -72,10 +74,14 @@ def discover_enabled(
         try:
             result[modname] = load_channel_class(modname)
         except ImportError as e:
-            logger.debug("Skipping built-in channel '{}': {}", modname, e)
+            message = "Enabled built-in channel '{}' is not available: {}"
+            if warn_import_errors:
+                logger.warning(message, modname, e)
+            else:
+                logger.debug(message, modname, e)
 
     external = discover_plugins(None if _include_all_external else enabled_names)
-    shadowed = set(external) & set(result)
+    shadowed = set(external) & set(names)
     if shadowed:
         logger.warning("Plugin(s) shadowed by built-in channels (ignored): {}", shadowed)
     if _include_all_external: