docs: Update slash commands documentation with official features

- Add comprehensive built-in commands reference (40+ commands)
- Document argument handling ($ARGUMENTS, $1, $2, etc.)
- Add bash execution syntax (! prefix) and file references (@ prefix)
- Update frontmatter to official fields (allowed-tools, argument-hint, model, etc.)
- Add Plugin Commands and MCP Slash Commands sections
- Add SlashCommand Tool documentation for programmatic invocation
- Add Skills vs Slash Commands comparison table
- Create commit.md example with bash execution and context
- Update existing examples to use official frontmatter format
- Add OpenSpec proposal for change tracking

01-slash-commands/push-all.md

@@ -1,7 +1,6 @@
 ---
-name: Commit and push everything
 description: Stage all changes, create commit, and push to remote (use with caution)
-tags: git, workflow, automation
+allowed-tools: Bash(git add:*), Bash(git status:*), Bash(git commit:*), Bash(git push:*), Bash(git diff:*), Bash(git log:*), Bash(git pull:*)
 ---
 
 # Commit and Push Everything