feat: Standalone preset storage, override permission hardening & bug fixes

- Extract presets into global presets.yaml; move editor to plugin main screen
- Add project-wide override sync and three-layer permission checks
- Fix embedding change detection, new-chat inheritance, and preset name leak bugs
- Clean up dead imports/params and fix description text

plugins/_model_config/default_config.yaml

@@ -31,27 +31,3 @@ embedding_model:
   kwargs: {}
 
 browser_http_headers: {}
-
-model_presets:
-  - name: "Efficiency"
-    chat:
-      provider: "openrouter"
-      name: "openai/gpt-5.2-chat"
-      api_key: ""
-      api_base: ""
-    utility:
-      provider: "openrouter"
-      name: "openai/gpt-5-nano"
-      api_key: ""
-      api_base: ""
-  - name: "Intelligence"
-    chat:
-      provider: "openrouter"
-      name: "anthropic/claude-opus-4.6"
-      api_key: ""
-      api_base: ""
-    utility:
-      provider: "openrouter"
-      name: "google/gemini-3-flash-preview"
-      api_key: ""
-      api_base: ""