feat(skills): install deepeval skill from confident-ai/deepeval

Adds the deepeval eval-loop skill via `npx skills add` with skills-lock.json
for reproducible reinstalls. Symlinked to Claude Code via .claude/skills/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016z2ZFYHQCex8yZAMVMTZzZ

.agents/skills/deepeval/references/choose-use-case.md

@@ -0,0 +1,46 @@
+# Choose Use Case
+
+Classify the target app before choosing templates, datasets, or metrics. Infer
+from code first; ask only when the code is ambiguous.
+
+## Top-Level Use Case
+
+Choose exactly one top-level use case:
+
+1. Chatbot or multi-turn agent
+2. Agent
+3. RAG
+4. Plain LLM
+
+Precedence rule:
+
+```text
+chatbot / multi-turn agent > agent > RAG > plain LLM
+```
+
+If the app is both RAG and agentic, classify it as an agent.
+
+If the app is both chatbot and agentic, classify it as chatbot / multi-turn
+agent.
+
+If the app is a chatbot backed by RAG, classify it as chatbot / multi-turn
+agent.
+
+## Signals
+
+| Use case | Signals in code | Test shape |
+| --- | --- | --- |
+| Chatbot / multi-turn agent | message history, chat endpoint, user session, turns, assistant role, multi-turn state | Multi-turn E2E |
+| Agent | tools, function calling, MCP tools, actions, planner, graph, LangGraph, CrewAI, PydanticAI | Single-turn E2E by default |
+| RAG | retriever, vector store, documents, chunks, context, citations, no higher-precedence chatbot or agent behavior | Single-turn E2E by default |
+| Plain LLM | one prompt in, one answer out, no tools or retrieval | Single-turn E2E |
+
+Use cases guide metrics and required trace fields. Templates are separated by
+test shape: single-turn tracing, single-turn no-tracing, and multi-turn E2E.
+Optional component/span metrics stay inside the single-turn tracing shape.
+
+## Dataset Default
+
+For chatbot or multi-turn agent use cases, generated datasets should be
+multi-turn by default. Use single-turn QA pairs only if the user explicitly says
+they want QA pairs for testing for now.