fix: replace ! with [BANG] in skill-development dynamic context examples

PR #192 introduced dynamic context injection documentation with literal
`!` backtick patterns that trigger shell execution during skill loading.
This replaces them with the [BANG] placeholder established in PR #142.

Fixes regression from feat: sync documentation (#192)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: sjnims

plugins/plugin-dev/skills/skill-development/SKILL.md

@@ -228,13 +228,13 @@ Execute commands to inject their output into skill context using backtick syntax
 ## Current Project Status
 
 The git status is:
-!`git status --short`
+[BANG]`git status --short`
 
 Recent commits:
-!`git log --oneline -5`
+[BANG]`git log --oneline -5`
 ```
 
-**Syntax:** `` !`command` ``
+**Syntax:** `` [BANG]`command` ``
 
 **Use cases:**