docs: the privacy policy moves into the repo

The policy lived only as prose inside the website's Astro page, so it was
the one user-facing document with no review, no history here, and no way
to change it alongside the code that makes it true.

docs/PRIVACY.md is now that text, transcribed from the published page so
the wording is unchanged, and it becomes the source: the site's build
checks this repository out beside itself and renders this file through an
Astro content collection rather than keeping its own copy. One copy of the
policy exists anywhere, so the two cannot drift.

The README links it from Documentation and gains a Privacy section beside
License. Agendula is being set up the same way.

README.md

@@ -157,6 +157,8 @@ reinstalling. Google Play is the exception — see above.</sub>
 - **[Building from source](docs/BUILDING.md)** — requirements and Gradle tasks
 - **[Architecture](docs/ARCHITECTURE.md)** — the layered design and key pipelines
 - **[Milestones](https://codeberg.org/jlmakiola/calendula/milestones)** — what's shipped and what's next
+- **[Privacy policy](docs/PRIVACY.md)** — the source of the page published at
+  [jeanlucmakiola.de/calendula/privacy](https://jeanlucmakiola.de/calendula/privacy)
 
 ## 🤝 Contributing
 
@@ -187,6 +189,16 @@ No coding needed — register on the Weblate server, pick (or request) a languag
 and translate the strings in your browser. You can also reach this link in the
 app from the top of **Settings → App language**.
 
+## 🔒 Privacy
+
+No analytics, no tracking, no advertising, no crash-reporting SDK, no third-party
+services — and **no internet permission at all**, so the app is technically
+incapable of transmitting anything anywhere. Your events stay in Android's own
+calendar store, where they already were.
+
+**→ [Privacy policy](https://jeanlucmakiola.de/calendula/privacy)** — written in
+[`docs/PRIVACY.md`](docs/PRIVACY.md), which is what that page renders.
+
 ## 📜 License
 
 [MIT](LICENSE) — Jean-Luc Makiola, 2026