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.

benchmarks/README.md

@@ -0,0 +1,34 @@
+# Model Benchmark Results
+
+CSV recordings from all model tests (chat, summary, embedding).
+
+## Files
+
+- `model_benchmarks.csv` — all benchmark results, one row per run per check
+
+## Schema
+
+| Column | Description |
+|---|---|
+| `date` | Test date (YYYY-MM-DD) |
+| `script` | `chat` | `summary` | `embed` |
+| `model` | Model name (e.g. `lite`, `turbo`, `embed`) |
+| `mode` | `fixture` / `derived` / `quality` / `dimension` / `cosine` / `speed` |
+| `gate_status` | `PASS` / `FAIL` |
+| `turns` | Number of questions/turns |
+| `answered` | Turns that produced an answer |
+| `caps` | Turns that hit the round cap |
+| `tool_turns` | Turns emitting ≥1 tool call (chat only) |
+| `emitted` / `executed` | Tool-call counts (chat only) |
+| `contract` | Numerator for accuracy (chat: well-formed calls; summary: quality 0–100; embed: 1=pass) |
+| `wall_s` | Total wall seconds |
+| `contract_denom` / `executed_denom` / `tool_turns_denom` | Denominators for percentages |
+| `extra1_col` / `extra1_val` | Script-specific metric 1 |
+| `extra2_col` / `extra2_val` | Script-specific metric 2 |
+
+## Scripts
+
+- `scripts/agent_realmodel_check.py` — chat model tool-calling battery
+- `scripts/test_summary_model.py` — summary model quality benchmark
+- `scripts/test_embed_model.py` — embedding model dimension/cosine/speed benchmark
+- `scripts/model_benchmark.py` — shared CSV recorder (imported by all scripts)