feat: nahual standalone — visores open-with sobre Llimphi (front-door, git-dep al monorepo)

Stack de visores extraído como front-door limpio: solo los crates nahual-*
(shell open-with + ~14 visores: texto/imagen/audio/video/svg/mapa/fuente/hex/
tabla/markdown/archivo/card/gallery/árbol + cores + meta-runtime). Todo lo
fundacional (discern, decoders media, fuentes content-addressed, hojas shared)
y Llimphi se consumen por git-dep del monorepo gioser.git — cero vendoring.
cargo check --workspace pasa (0 errores).

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

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Sergio
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.