fix(core,gui,cli): a blocked sign-in no longer asks to update the app (B209)

Proton answers a sign-in it blocks for abuse or rate limits with code
2028 and the text "This version of the app is no longer supported". The
SDK read 2028 as Unknown, so the app passed that text through and told
users to update a current release (issues #28, #39).

- deps: proton-sdk and proton-drive-rs 0.8.3, which name 2028 Blocked
- core: error::sign_in_blocked detects it
- gui: the login page says Proton is refusing sign-in for now and that
  waiting helps, translated in every catalog
- cli: pdfs login adds the same hint to the error
- cli: pdfs diagnose warns instead of failing when cache.db does not
  exist yet; the daemon creates it after the first sign-in
- docs: BUGS.md B209, changelog, troubleshooting entry

docs/CHANGELOG.md

@@ -11,6 +11,14 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
 
 ## [Unreleased]
 
+### Fixed
+- **A blocked sign-in said the app version was no longer supported.** Proton refuses sign-in for
+  a while after it suspects abuse, and its message then asks you to update. The app and
+  `pdfs login` now say that Proton is refusing sign-in for now and that waiting helps
+  (B209, [#39](https://github.com/narrrl/proton-drive-linux/issues/39)).
+- **`pdfs diagnose` failed the `database` check on a fresh install.** The daemon creates the
+  database after the first sign-in, so a missing one is now a warning.
+
 ## [3.4.0] — 2026-10-12
 
 Schema: **42**, unchanged.