Add the backend contract and session-domain support for
'Branch from here':
- new branchSession IPC method and sessions:branch channel
- branchOrigin metadata on SessionRecord
- session branching helper that truncates the transcript at a
chosen user message and clears runtime state
- AryxAppService branching flow with scratchpad directory support
- persistence normalization and regression coverage
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Add persisted session and pattern metadata for pinning, archiving, manual titles, and favorite patterns. Expose backend query and mutation APIs for session library features, and cover the shared helpers with tests.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
