feat(web): lien « Buy me a coffee » (nav, réglages, funding)

- constante BUYMEACOFFEE_URL ; item de nav « Offrez-moi un café »
- section support dans les Réglages + i18n EN/FR
- champ `funding` dans le package.json publié ; mentions README EN/FR

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

README.md

@@ -255,6 +255,12 @@ node packages/server/scripts/acceptance-p4.mjs   # Web Push + WS `answer` comman
 node packages/server/scripts/acceptance-p5.mjs   # work groups: CRUD + WS broadcast + CASCADE
 ```
 
+## Support
+
+Arboretum is a free, self-funded side project. If it saves you time, you can support its development:
+
+[![Buy Me a Coffee](https://img.shields.io/badge/Buy%20Me%20a%20Coffee-johanleroy-FFDD00?logo=buymeacoffee&logoColor=black)](https://buymeacoffee.com/johanleroy)
+
 ## License
 
 MIT — see [LICENSE](LICENSE).