Reorganize brain: projects/ top level, rename filenames, update homepage

- Moved everything from ideas/passepartout/ to projects/passepartout/
- Moved legal structures to projects/flags/
- Created missing _index.org files for all subdirectories
- Stripped redundant passepartout- prefix from filenames
- Rewrote root _index.org as generalized brain index (projects + concepts)
- Updated Hugo nav to Projects/Concepts
- Updated build script section descriptions
- Deleted stale ideas/passepartout-economics.md orphan

projects/passepartout/strategy/compliance/_index.org

@@ -0,0 +1,7 @@
+#+title: Compliance
+#+filetags: :compliance:index:
+
+:PROPERTIES:
+:CREATED:  [2026-05-24 Sun]
+:ID:       1c4c91ec-c465-44ab-bd91-4c3b45909ddb
+:END: