Custom agents flag, in-file keyword search, and Jujutsu diff fixes

Added --agent flag, in-file keyword search for artifacts, recursive subagent updates, and Jujutsu workspace diff fixes.

• Added the --agent flag and agent/agents subcommand, allowing users to select a custom agent at launch and list available agents.
• Added in-file keyword search (/) and jump navigation (n/N) to the artifact detail viewer, allowing users to find and cycle through matches without disrupting terminal escape sequences or image grids.
• Added support for displaying nested subagents (grandchild and deeper) and handling tool confirmation requests across all subagent depths by recursively relaying nested subtrajectory updates to the root conversation.
• Changed the default mode to respect write_file permissions allowlisted in settings.json under permission.allow, so pre-approved file writes no longer prompt for review.
• Changed the default name for the newly initialized project to CLI Project for clearer workspace identification.
• Improved the session exit output by placing the resume command on its own line, making it easier to copy and paste in terminals and tools like tmux.
• Fixed print mode (--print / -p) silently exiting with a success code and empty output when a request failed server-side, now writing the error to stderr and returning a non-zero exit code.
• Fixed agy -p hanging when run inside a shell script or subprocess by no longer reading stdin when a prompt is provided via a flag.
• Fixed a data race on the /btw cancellation function.
• Fixed interactive /diff viewer defects in Jujutsu (jj) workspaces by correctly prioritizing .jj over .git in colocated repos, fixing commit hash regex boundaries, and correctly highlighting active @ graph nodes.
• Fixed workspace-local hooks defined in /.agents/hooks.json not loading after trusting a folder by reloading hooks whenever workspaces change.
• Fixed misaligned markdown tables containing file links in chat output.