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/artifact-contracts.md

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+# Artifact Contracts
+
+Create eval artifacts that users can inspect, edit, commit, and rerun without
+an agent.
+
+## Preferred Layout
+
+```text
+tests/
+  evals/
+    test_<app>.py
+    metrics.py
+    .dataset.json
+```
+
+Use an existing eval directory if the project already has one.
+
+First look for an existing test folder. If one exists, put the eval suite there.
+If none exists, create `tests/evals/`.
+
+Prefer one eval test file for the first setup. Component/span metrics belong in
+the same single-turn tracing file. Add more files only for a clearly distinct
+use case.
+
+## Dataset Files
+
+Preferred generated dataset path:
+
+```text
+tests/evals/.dataset.json
+```
+
+Use `.dataset.json`, not `goldens.json`. The mental model is: a dataset contains
+goldens.
+
+Supported input formats:
+
+- `.json`
+- `.jsonl`
+- `.csv`
+
+The dataset should contain the fields needed by the chosen template and metrics.
+For RAG, include context or enough information to reconstruct context from the
+app. For multi-turn evals, use conversational goldens.
+
+## Pytest Files
+
+Eval tests should:
+
+- load the dataset from `tests/evals/.dataset.json` by default
+- call the real app entry point
+- prefer native DeepEval integrations and traced `Golden` assertions
+- build `LLMTestCase`s only in explicit no-tracing evals
+- import a small, explicit metric list from `metrics.py`
+- add span-level metrics only for useful component diagnostics
+- use existing metrics and thresholds when found
+- avoid network calls unrelated to the app or evaluation model
+- be run with `deepeval test run`, not the raw `pytest` command
+
+## Placeholder Contract
+
+Templates intentionally contain placeholders:
+
+- dataset file paths in `add_goldens_from_*_file(...)`
+- AI app module/function names such as
+  `import_module("ai_app").run_traced_ai_app`
+- metric lists in `metrics.py`
+- integration callback/instrumentation setup when applicable
+
+Replace every placeholder before running evals. If a placeholder remains, stop
+and adapt the template instead of running a broken suite.
+
+## Result Artifacts
+
+Do not create hidden result caches unless DeepEval already does so. The durable
+artifacts are the test files, dataset files, tracing integration, and optional
+Confident AI hosted reports.