docs: Add blog post and new slash commands for development workflow

- Add blog post: 4 Essential Slash Commands I Use in Every Project
- Add new slash commands: /doc-refactor, /setup-ci-cd, /unit-test-expand
- Update slash-commands README with comprehensive documentation
- Simplify /push-all command structure
- Archive add-blog-post-slash-commands change
- Add blog-post spec and pending openspec changes

openspec/changes/archive/2025-12-26-add-blog-post-slash-commands/proposal.md

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+# Change: Add Blog Post - 4 Essential Slash Commands for Development Workflow
+
+## Why
+
+The claude-howto project provides excellent reference documentation but lacks blog-style content that showcases real-world usage patterns. Users have found 4 slash commands particularly valuable across their development workflow, and a blog post explaining when/where/how to use each would help others adopt these productivity tools.
+
+## What Changes
+
+- Create new `blog-post/` directory for blog content
+- Add blog post: "4 Essential Slash Commands I Use in Every Project"
+- Cover 4 commands with practical guidance:
+  - `/push-all` - Quick deployment of coherent changes
+  - `/setup-ci-cd` - Post-POC quality infrastructure
+  - `/doc-refactor` - Post-MVP documentation polish
+  - `/unit-test-expand` - Milestone-driven test expansion
+- Reference the first slash commands blog: [Discovering Claude Code Slash Commands](https://medium.com/@luongnv89/discovering-claude-code-slash-commands-cdc17f0dfb29)
+- Link to full command files when content exceeds 30 lines
+
+## Impact
+
+- Affected specs: None (new capability)
+- Affected code: New `blog-post/` directory and content
+- No breaking changes