chore: track the design docs in git (.gitignore !*.md)

AUDIT P1: every markdown design doc except CODEMAP.md was untracked, so
ARCHITECTURE / AUDIT / OPSTACK-PLAN / fable-idea / REVIEW_FINDINGS lived
only on disk. Replaces the single !CODEMAP.md exception with !*.md.

Also makes OPSTACK-PROGRESS.md commits actually record something, which
the unattended crash-safety discipline depends on.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitignore

@@ -10,4 +10,6 @@
 !/Source/**
 
 !VoxelForge.uplugin
-!CODEMAP.md
+
+# Keep every design / doc markdown at any depth (AUDIT P1 — these were untracked)
+!*.md