feat: khipu standalone — notas P2P soberanas content-addressed, local-first (front-door, git-dep al monorepo)

Front-door limpio: solo crates del dominio; Llimphi y lo fundacional por
git-dep del monorepo gioser.git. cargo check pasa (5 crates, 0 errores).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,3 @@
+/target
+**/*.rs.bk
+*.pdb