chore: remove vibe-coding artifacts from tracking, sync notes and obsidian config

- Untrack .claude/launch.json (Claude Code config)
- Add .claude/, .mcp.json, CLAUDE.md, and AI-generated CSVs to .gitignore
- Add _notes/ vault (architecture, API, tasks, bugs, infra docs)
- Add .obsidian/ plugin/vault config (workspace state excluded)
- Sync CHANGELOG.md

_notes/05 - Tasks & Planning/Backlog.md

@@ -0,0 +1,16 @@
+# Backlog
+
+> Use this for longer-form feature/task descriptions. Move short tasks to [[Kanban]].
+
+## Features to Build / Improve
+- [ ]
+
+## Documentation to Write
+- [ ] API endpoint reference
+- [ ] Onboarding guide for new contributors
+
+## Bugs to Fix
+> See [[06 - Bugs & Issues/Bug Log]]
+
+## Ideas
+- [ ]