Fix internal error when enabling a plugin

enable_plugin called register_blueprint at runtime, which Flask forbids after
the first request (AssertionError -> 500). Enabling now flips the registry flag
and fires on_enable best-effort; routes register on the next restart, symmetric
with disable. Nav reflects the re-enable immediately.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shopdb/plugins/__init__.py

@@ -257,11 +257,16 @@ class PluginManager:
 
         self.registry.enable(name)
 
-        # Load the plugin
-        plugin = self.loader.load_plugin(name, self._app, self._db)
-        if plugin:
-            self._register_plugin_components(plugin)
-            plugin.on_enable(self._app)
+        # Fire the on_enable hook best-effort. Do NOT register the blueprint
+        # here: Flask forbids register_blueprint after the first request, so
+        # routes/nav for a re-enabled plugin take effect on the next restart
+        # (symmetric with disable).
+        try:
+            plugin = self.loader.load_plugin(name, self._app, self._db)
+            if plugin:
+                plugin.on_enable(self._app)
+        except Exception:
+            logger.exception(f"on_enable hook failed for plugin {name}")
 
         logger.info(f"Enabled plugin: {name}")
         return True