docs: complete CHANGELOG.md with missing historical versions

- Add standard Keep a Changelog header with format description
- Add Unreleased section following standard format
- Add comprehensive entries for versions 0.1.0, 0.2.0, and 0.3.0
- Research and document historical features using git log analysis
- Follow Keep a Changelog categories (Added, Changed, Fixed)
- Maintain chronological order with proper release dates
- Update TODO.md to reflect completed changelog enhancement work

🤖 Generated with [Claude Code](https://claude.ai/code)

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

TODO.md

@@ -0,0 +1,43 @@
+# Todofile
+
+This is a "to do next" file, particularly useful to keep the human and a coding assistant in sync.
+
+The format is based on [Keep a Todofile V0.0.1](https://coulomb.social/open/KeepaTodofile).
+
+The structure organizes **future tasks** by their impact, just as a changelog organizes past changes by their impact.
+
+***
+
+## [Unreleased] - *Active Vibe-Coding State* 💡
+
+This section is for tasks currently being discussed with or worked on by the coding assistant. These are the ephemeral, flow-of-thought tasks.
+
+* **To Add:**
+    * None currently identified
+
+* **To Fix:**
+    * None currently identified
+
+* **To Refactor:**
+    * None currently identified
+
+* **To Remove:**
+    * None currently identified
+
+***
+
+## Completed Tasks
+
+**CHANGELOG.md Enhancement - COMPLETED ✅**:
+- ✅ Added missing version entries for 0.1.0, 0.2.0, and 0.3.0
+- ✅ Added standard Keep a Changelog header with proper format
+- ✅ Included Unreleased section
+- ✅ Research completed for all historical versions using git log analysis
+- ✅ All entries follow Keep a Changelog categories (Added, Changed, Fixed)
+- ✅ Chronological order maintained with latest versions first
+- ✅ Appropriate release dates included based on git commit timestamps
+
+**Version Details Added**:
+- v0.1.0 (2025-10-15): Development infrastructure, TDD workspace, issue management
+- v0.2.0 (2025-10-20): Advanced Markdown Engine with GraphQL, search, plugins
+- v0.3.0 (2025-10-25): Architectural improvements with kaizen-agentic integration