* feat: client-side knock auto-accept via KnockTracker
Replace server-side AutoAcceptInviteIfKnocked (removed in
synapse-pangea-chat PR #21) with client-side KnockTracker.
- Record knocked room IDs in Matrix account data (org.pangea.knocked_rooms)
- Auto-join when invite arrives for a previously knocked room
- Migrate storage from GetStorage to Matrix account data for
cross-device sync and reinstall persistence
- Add joining-courses.instructions.md design doc
* formatting
* centralizes calls to knock-storage related functions
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Co-authored-by: ggurdin <ggurdin@gmail.com>