refactor(web): split api_v3/plugins.py by area

web_interface/blueprints/api_v3/plugins.py (3,285 lines) becomes:
- plugins.py: installed list, enable/disable, plugin actions
- plugin_store.py: install, update, uninstall, store, saved repositories
- plugin_config.py: config get/save, schema, reset
- plugin_assets.py: asset uploads and plugin static files
- plugin_health.py: health, metrics, limits
- plugin_operations.py: operation history, state reconciliation
- plugin_calendar.py: calendar credentials and auth

Pure move: all 44 functions and 38 route decorators are byte-identical
(checked with ast), URLs and endpoint names are unchanged (url-map test).
Each module imports only what it uses. Tests and config.py that reached
into plugins.py for moved names now import from the new module.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/test_api_v3_upload_writes.py

@@ -25,7 +25,7 @@ PNG = b"\x89PNG\r\n\x1a\n" + b"0" * 20
 
 @pytest.fixture
 def project(tmp_path, api_v3_module, monkeypatch):
-    import web_interface.blueprints.api_v3.plugins as plugins_module
+    import web_interface.blueprints.api_v3.plugin_assets as plugins_module
     monkeypatch.setattr(plugins_module, "PROJECT_ROOT", tmp_path)
     return tmp_path / "assets" / "plugins" / "static-image" / "uploads"
 

test/test_path_traversal_guards.py

@@ -281,7 +281,7 @@ class TestPluginAssetRoutes:
 
     @pytest.fixture
     def project(self, tmp_path, api_v3_module, monkeypatch):
-        import web_interface.blueprints.api_v3.plugins as plugins_module
+        import web_interface.blueprints.api_v3.plugin_assets as plugins_module
 
         monkeypatch.setattr(plugins_module, "PROJECT_ROOT", tmp_path)
         (tmp_path / "config").mkdir()

test/web_interface/test_normalize_nullable_structural_types.py

@@ -15,7 +15,7 @@ import logging
 
 import pytest
 
-from web_interface.blueprints.api_v3.plugins import (
+from web_interface.blueprints.api_v3.plugin_config import (
     _prepare_plugin_config_for_save,
 )