* feat(agent): add standalone agent runtime
* fix(agent): add Bun and DOM types to agent tsconfig
* refactor: wrap backup error in a tagged effect error
* feat(controller): add agent manager and session handling
* feat(backups): execute backups through the agent
* fix(agent): harden disconnect and send-failure handling
* fix: rebase conflicts
* test: simplify mocks
* refactor: split agent runtime state
* fix(backup): keep old path when agent is disabled
* fix: pr feedbacks
