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/commit.md

@@ -0,0 +1,26 @@
+---
+allowed-tools: Bash(git add:*), Bash(git status:*), Bash(git commit:*), Bash(git diff:*)
+argument-hint: [message]
+description: Create a git commit with context
+---
+
+## Context
+
+- Current git status: !`git status`
+- Current git diff: !`git diff HEAD`
+- Current branch: !`git branch --show-current`
+- Recent commits: !`git log --oneline -10`
+
+## Your task
+
+Based on the above changes, create a single git commit.
+
+If a message was provided via arguments, use it: $ARGUMENTS
+
+Otherwise, analyze the changes and create an appropriate commit message following conventional commits format:
+- `feat:` for new features
+- `fix:` for bug fixes
+- `docs:` for documentation changes
+- `refactor:` for code refactoring
+- `test:` for adding tests
+- `chore:` for maintenance tasks