feat: add hook_context kwarg to save_plugin_config and get_plugin_config extensible calls

Adds hook_context: dict kwarg to both call_plugin_hook() call sites in
save_plugin_config() and get_plugin_config() in helpers/plugins.py.

Motivation:
Plugins intercepting these hooks have no way to distinguish the caller context
(UI display vs service layer vs agent). Without this, plugins that need to
behave differently per caller (e.g. a secrets manager that masks values for UI
but resolves them for services) cannot do so without fragile inspect.stack() hacks.

hook_context is a free-form dict. Existing plugin hooks receive it via **kwargs
and can ignore it — fully backwards compatible.

Callers pass e.g. {"caller": "ui"}, {"caller": "service"}, {"caller": "agent"}.

This is a universal utility, not specific to any one plugin.

Author: Deimos-Agent

helpers/plugins.py

@@ -629,6 +629,7 @@ def get_plugin_config(
         agent=agent,
         project_name=project_name,
         agent_profile=agent_profile,
+        hook_context={"caller": "api"},
     )
 
     return result
@@ -669,6 +670,7 @@ def save_plugin_config(
         project_name=project_name,
         agent_profile=agent_profile,
         settings=settings,
+        hook_context={"caller": "api"},
     )
 
     # or do standard load