chore: point Bravais reference at Steelbore/Bravais

Bravais (the NixOS module loaded in v1.0.0 §6.6) has moved from the
personal namespace to `github:Steelbore/Bravais` (capital B).

Updates the v1.0.0 TODO breadcrumb in flake.nix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: UnbreakableMJ <34196588+UnbreakableMJ@users.noreply.github.com>

Author: UnbreakableMJ

flake.nix

@@ -89,7 +89,7 @@
 
         # Stub package — actual release builds come from `cargo build` driven
         # by .github/workflows/release.yml; v1.0.0 §6.6 of TODO.md installs the
-        # NixOS module under github:UnbreakableMJ/bravais.
+        # NixOS module under github:Steelbore/Bravais.
         packages = { };
       });
 }