docs: re-sync README.es.md to current English (agentic numbers, CodeWhale)

The Spanish README merged (#110) carrying stale content: the old flat
"80-94% menos código" single-shot headline (the exact claim #126 corrected),
no CodeWhale section, badge stuck at 13 agents, and missing the Modern Web
Guidance callout (#82) and the Claude Code desktop-install paragraph.

Re-translates the hero + Números section to the corrected agentic numbers
(~54%, up to 94%, 100% safe) with the old figures demoted to the same
<details> block English uses, adds CodeWhale, fixes the badge, and adds a
"community translation, English is the reference" note. Also adds a minimal
Español discoverability link to the English README so readers can find it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -23,6 +23,10 @@
   <sub>Measured on real Claude Code sessions editing a real open-source repo (FastAPI + React), against the same agent with no skill. ~54% is the mean across 12 feature tasks (Haiku 4.5, n=4); it reaches 94% where an agent over-builds (a date picker) and is near zero where the code is already minimal. ponytail keeps every safety guard while a bare "write one-liners" prompt drops one. (The earlier single-shot benchmark reported 80-94% as a flat figure; against a fair agentic baseline that is the per-task ceiling, not the average.) <a href="benchmarks/results/2026-06-18-agentic.md">Full writeup</a> &middot; <a href="benchmarks/">reproduce it</a>.</sub>
 </p>
 
+<p align="center">
+  <sub><a href="README.es.md">Español</a></sub>
+</p>
+
 ---
 
 You know him. Long ponytail. Oval glasses. Has been at the company longer than the version control. You show him fifty lines; he looks at them, says nothing, and replaces them with one.