feat(agent): add CSV benchmark recorder + summary/embedding test scripts and skills

New files:
- scripts/model_benchmark.py — shared CSV recorder for all model tests
- scripts/test_summary_model.py — summary model quality benchmark (coherence, coverage, brevity, hallucination)
- scripts/test_embed_model.py — embedding model benchmark (dimension, cosine accuracy, speed)
- .agents/skills/test-summary-model/SKILL.md — skill for testing summary models
- .agents/skills/test-embed-model/SKILL.md — skill for testing embedding models
- benchmarks/README.md — schema documentation

Updated:
- .agents/skills/test-chat-model/SKILL.md — now also records to CSV

All three scripts write to benchmarks/model_benchmarks.csv with one row
per run per check. The CSV accumulates results across runs for comparison.

.agents/skills/test-chat-model/SKILL.md

@@ -96,18 +96,34 @@ prints the `MISS` lines naming the condition. Interpret:
 - **caps > 0** — the phase-72 incident signature; a real regression,
   say so explicitly.
 
-### 5. Record + commit
+### 5. Record to CSV + commit
 
-Append the model's results to the model-comparison subsection of
-`TOOL_CALLING_TESTING.md` §3, keeping the `gate:` lines **byte-exact
-verbatim**, plus 2–4 sentences of interpretation against the reference
-rates above and the wall-time baseline (lite ~43–55 s, turbo ~105–135 s
-per full loop).
+**a. CSV record** — append to `benchmarks/model_benchmarks.csv` via
+`scripts/model_benchmark.bench_write`. For each of the 3 runs, call:
+
+```python
+from scripts.model_benchmark import bench_write
+
+bench_write(
+    script="chat", model="<model>", mode="fixture",
+    gate_status="PASS", turns=10, answered=10, caps=0,
+    tool_turns=<N>, emitted=<E>, executed=<X>,
+    contract=<C>, wall_s=<wall>,
+    contract_denom=<C_denom>, executed_denom=<E_denom>,
+)
+```
+
+For the derived run, use `mode="derived"`.
+
+**b. Append to TOOL_CALLING_TESTING.md** — keep the `gate:` lines
+**byte-exact verbatim**, plus 2–4 sentences of interpretation against
+the reference rates above and the wall-time baseline (lite ~40–55 s,
+turbo ~97–135 s per full loop).
 
 Commit — docs only, house style:
 
 ```bash
-git add TOOL_CALLING_TESTING.md
+git add TOOL_CALLING_TESTING.md benchmarks/model_benchmarks.csv
 git commit --no-gpg-sign \
   -m "docs(agent): record the <model> comparison on the controlled fixture battery" \
   -m "<one-paragraph body: the numbers, the re-read rate, the wall time, any MISS nuance>"