feat(licensing): adopt GFDL-1.3+ for presentations and MIT for build tooling

- Establish dual licensing: GNU Free Documentation License v1.3 or later (no invariants) for slides, documentation, and diagrams
- License automation scripts, Makefiles, CSS/JS templates, and Lua filters under the MIT License
- Implement REUSE compliance with LICENSES/ directory and machine-readable SPDX headers across all project files
- Document licensing terms and DCO contribution requirements in README.rst and CONTRIBUTING.rst
- Update Schema.org JSON-LD metadata and closing slide with canonical GNU FDL references

Co-developed-by: Antigravity <antigravity@google.com>
Signed-off-by: Rénich Bon Ćirić <renich@woralelandia.com>

general/html/seo_head.html

@@ -95,7 +95,7 @@
         "@id": "https://mx-os.mx/#organization"
       },
       "image": "https://presentaciones.mx-os.mx/general/images/og-image.png",
-      "license": "https://creativecommons.org/licenses/by-sa/4.0/",
+      "license": "https://www.gnu.org/licenses/fdl-1.3.html",
       "about": [
         {"@type": "Thing", "name": "Soberanía Tecnológica"},
         {"@type": "Thing", "name": "Linux"},