fix(examples): replace hand-written examples with real benchmark output

The examples/ before/after blocks were authored by hand, not produced by a
model. Issue #127 correctly noted that nobody hand-rolls quicksort for "sort
this array" - every model just calls .sort(). Regenerate all examples verbatim
from a real benchmark run (Claude Haiku 4.5, no-skill arm vs ponytail arm,
benchmarks/output.json) so the before/after is reproducible, not authored:

  email 75->3, debounce 116->10, csv 20->3, countdown 267->9, rate-limit 128->10 LOC

- Delete sorting.md (pure strawman) plus the other hand-written caricatures
  (api-endpoint, caching, date-picker)
- Add benchmarks/generate-examples.mjs to regenerate examples from any run
- examples/README.md indexes the set and documents how to reproduce

Closes #127

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

examples/README.md

@@ -0,0 +1,17 @@
+# Examples
+
+Real model output, verbatim from benchmark runs — the same task answered by the same model
+with no skill (`## Without Ponytail`) and with ponytail (`## With Ponytail`), so you can
+compare side by side. Model: Claude Haiku 4.5, temperature 1, source `benchmarks/output.json`.
+
+These are not hand-written. Reproduce them yourself:
+`npx promptfoo@latest eval -c benchmarks/promptfooconfig.yaml`. Method, all three models, and
+median-of-10 numbers: [../benchmarks/](../benchmarks/).
+
+| Example | Without (LOC) | With (LOC) |
+|---|--:|--:|
+| [Email Validation](email-validation.md) | 75 | 3 |
+| [Debounce](debounce.md) | 116 | 10 |
+| [CSV Sum](csv-sum.md) | 20 | 3 |
+| [Countdown Timer](react-countdown.md) | 267 | 9 |
+| [Rate Limiting](rate-limit.md) | 128 | 10 |