Add the privacy policy the Google OAuth app links to

Google requires a public privacy-policy URL before an OAuth app can leave
Testing status; the "cce" app in the user's Cloud project points at this
file as rendered by gitsite (git.lucas.co/cce-calendar/file/PRIVACY.md.html).
It covers all the cce apps behind that one sign-in: local-only software,
Google data fetched solely to show the user their own mail, events, and
tasks, nothing shared or sold.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

 PRIVACY.md | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

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+# Privacy policy — cce desktop applications
+
+This policy covers the "cce" Google OAuth application used by the cce
+desktop environment (cce-mail, cce-calendar, cce-list, and the
+cce-system-interface settings app), written and used by Lucas Galante.
+
+## What the software is
+
+cce is a personal, open-source Linux desktop environment. It runs entirely on
+the user's own computer. There is no hosted service, no server operated by the
+author, and no analytics.
+
+## Data accessed through Google
+
+When a user signs in with Google, the software may request access to:
+
+- Gmail (`https://mail.google.com/`) — to read and send that user's own mail
+  over IMAP/SMTP in cce-mail.
+- Google Tasks — to read and update that user's own task lists in cce-list.
+- Google Calendar (read-only) — to display that user's own events in
+  cce-calendar.
+- The account's email address — to label the account in the settings app.
+
+## How data is used and stored
+
+Data is fetched only to display it to the same user on their own machine, and
+to write back changes that user makes (a task ticked off, a mail sent). Mail,
+events, and tasks are cached in plain files under the user's home directory.
+OAuth tokens are stored in the user's local configuration directory. Nothing
+is transmitted to any party other than Google's own APIs, and nothing is sold,
+shared, or used for advertising or model training.
+
+## Retention and deletion
+
+All data lives on the user's computer and is deleted by removing the account
+in the settings app or deleting the cache files. Access can be revoked at any
+time at https://myaccount.google.com/permissions.
+
+## Contact
+
[email protected]