* fix: strip origin/ prefix from base branch for rebase/merge operations
The frontend was passing 'origin/main' as the base branch, but the backend
expects just the branch name (e.g., 'main') and constructs 'origin/' itself.
This caused git fetch to fail with:
fatal: couldn't find remote ref origin/main
Because the command became 'git fetch origin origin/main' instead of
'git fetch origin main'.
* fix: increase prompt timeout to 60min, add error feedback, rename acp to agent API
- Add PromptTimeout constant (60 minutes) in common/constants/timeouts.go
- Update agentctl client and server to use the constant
- Add error message creation when prompt fails (timeout, agent not running, etc)
- Rename /acp/* endpoints to /agent/* (protocol-agnostic naming)
- Rename acp.go files to agent.go in both client and server
- Rename handler functions from handleACP* to handleAgent*
João Salavisa