feat(llm): mask API keys in UI responses and prevent masked-key leakage in fetch/test/save payloads

- Add mask_api_key() and is_masked_or_placeholder() to llm_provider service
- Return masked keys in all provider CRUD endpoints
- Reject masked/placeholder keys in fetch_models and test_provider_config
- Show masked key with Change button in ProviderConfig.svelte edit form
- Exclude masked keys from fetch-models, test, and submit payloads on frontend
- Update semantics-core skill with clarified complexity tier rules
- Switch agent modes from subagent to all

docs/openapi/litellm/chunks_meta.json

@@ -0,0 +1,11 @@
+{
+  "openapi": "3.1.0",
+  "info": {
+    "title": "llm.rusal.com",
+    "description": "Enterprise Edition \n\nProxy Server to call 100+ LLMs in the OpenAI format. [**Customize Swagger Docs**](https://docs.litellm.ai/docs/proxy/enterprise#swagger-docs---custom-routes--branding)\n\n\ud83d\udc49 [```LiteLLM Admin Panel on /ui```](/ui). Create, Edit Keys with SSO. Having issues? Try [```Fallback Login```](/fallback/login)\n\n\ud83d\udcb8 [```LiteLLM Model Cost Map```](https://models.litellm.ai/).\n\n\ud83d\udd0e [```LiteLLM Model Hub```](/ui/model_hub_table). See available models on the proxy. [**Docs**](https://docs.litellm.ai/docs/proxy/ai_hub)\n\n\ud83d\udcac [```LiteLLM Chat UI```](/ui/chat). ChatGPT-like interface for your users to chat with AI models and MCP tools.",
+    "version": "1.83.7"
+  },
+  "servers": [],
+  "tags": [],
+  "externalDocs": {}
+}