feat(optimize): share the efficiency objective

autotune, autoskill and confidence each carried their own idea of what an
improvement is, and autotune's two efficiency rules were the same sentence
twice. They now route to one skill that names three axes to move at once —
fewer tokens, less time, higher quality — and the rules that decide when a
proposal counts: at least one axis better, none damaged, quality never the
currency, observed friction instead of a guessed percentage.

Applying its own rule, autotune gets shorter rather than longer. The test
holds the coupling, so a later rewrite cannot silently drop a route.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

skills/autoskill/SKILL.md

@@ -7,6 +7,10 @@ description: >
   and the pattern is general enough to reuse. Portable across projects.
 ---
 
+Its objective is the `optimize` skill's: a skill is worth creating only when it
+cuts tokens or time and raises quality — judge every candidate against that
+skill's three axes and rules.
+
 When you notice the operator repeating the same kind of instruction,
 correction, or prompt pattern (about three occurrences, exact wording may
 vary), do the following: