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

.gitignore

@@ -52,3 +52,20 @@ web/assets/login-bg.mp4
 *.keystore
 # large binary assets — keep local only, not tracked in git
 assets/login-bg.mp4
+
+# Obsidian — exclude personal workspace state, keep plugin/vault config
+.obsidian/workspace.json
+.obsidian/workspace-mobile.json
+.obsidian/cache
+
+# Claude Code / MCP / vibe-coding tool artifacts
+.claude/
+.mcp.json
+CLAUDE.md
+hero_section_improvements.csv
+security_audit_report.csv
+feature_gap_analysis.csv
+
+# Obsidian workspace state in nested vaults
+**/.obsidian/workspace.json
+**/.obsidian/workspace-mobile.json