Synaplan Channels Update v4.2.2

Updated some OIDC flow and the Dropbox integration mainly besides smaller fixes:

What's Changed

• fix(backend): stop routing chat at models that were retired upstream by @cristiangrxs in #1513
• feat(models): detect discontinued provider models before users hit them by @FExB17 in #1512
• feat: GUEST_CHAT_ENABLED switch for the anonymous guest trial by @dschmidt in #1518
• fix: auto-redirect expired OIDC sessions back to the IdP by @dschmidt in #1519
• fix(config): container-safe defaults for strictly-bound env vars by @dschmidt in #1522
• feat(models): detect AI model outages and show them on a status page by @cristiangrxs in #1516
• fix: Dropbox upload, mobile History link, and no-provider chat tombstone by @orgaralf in #1521

Full Changelog: v4.2.1...v4.2.2