chore(agents): require Strunk and White conciseness in rule-creator (#4240)

Agent rules should be brief and direct so they do not bloat context.
Update the formatting guidelines in the rule-creator skill to require
Strunk and White conciseness ("Omit needless words").

.agents/skills/rule-creator/SKILL.md

diff --git a/.agents/skills/rule-creator/SKILL.md b/.agents/skills/rule-creator/SKILL.md
index 9ed7978..1d0f9cd 100644
--- a/.agents/skills/rule-creator/SKILL.md
+++ b/.agents/skills/rule-creator/SKILL.md
@@ -38,7 +38,8 @@
 *   **Line Wrapping:** Always wrap all text in the rule file (including the
     title and description) to **80 columns** to ensure readability and
     compatibility.
-*   **Clarity:** Write clear, actionable directives.
+*   **Conciseness (Strunk & White):** Omit needless words. Write brief, direct,
+    actionable directives without filler prose.
 
 ### Example