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/competitors/_index.org

@@ -0,0 +1,8 @@
+:PROPERTIES:
+:CREATED:  [2026-05-24 Sun]
+:ID:       0d4e5f6a-7b8c-9d0e-1f2a-3b4c5d6e7f8a
+:END:
+#+title: Passepartout — Competitive Analysis
+#+filetags: :index:
+
+Competitive analysis of AI coding agents, verification platforms, and the broader infrastructure landscape.