Integrate tectonix zones with lazy-trees infrastructure

Add native git repository access for world/tectonix monorepo support:

- New builtins for zone manifest access (__unsafeTectonixInternalManifest,
  __unsafeTectonixInternalManifestInverted) and tree fetching
  (__unsafeTectonixInternalTree)
- Lazy mounting for zones: clean zones use git tree accessors,
  dirty/checkout zones use filesystem accessors
- Zone path validation ensuring paths match exact manifest roots
- Support for odbOnly mode in git-utils for repositories with
  unsupported extensions like reftables
- Dirty zone detection via git status integration
- Caching for zone accessors and manifest content

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: burke

CLAUDE.md

@@ -0,0 +1,5 @@
+build with:
+
+```
+nix develop -c meson compile -C build
+```