cleanup: remove stale .mindmodel, old venvs, orphaned code, and transient artifacts

Removes:
- .mindmodel/ directory and related CI workflows (mindmodel-schedule.yml, mindmodel-validation.yml)
- scripts/mindmodel/ and scripts/validate_mindmodel.py
- src/types/ and src/validators/ (orphaned type modules, only used by mindmodel)
- tests/ci/, tests/scripts/mindmodel/, tests/types/, tests/validators/ (mindmodel-only tests)
- thoughts/ledgers/ and thoughts/shared/ (stale transient directories)
- .venv_axis and .venv_plotly (orphaned virtual environments, ~1.1 GB)
- outputs/blog-charts/ (stale generated HTML files)
- data/*.json sidecars (empty cache artifacts)
- __pycache__ and *.pyc files across repo

Updates:
- .gitignore: remove thoughts/shared/analyses/ entry

Space reclaimed: ~1.1 GB+

.gitignore

@@ -29,7 +29,6 @@ dummy
 # Generated analysis files
 thoughts/explorer/*.json
 thoughts/explorer/*_report.md
-thoughts/shared/analyses/
 
 # Compound Engineering local config
 .compound-engineering/*.local.yaml