docs: rebrand as tmux fork with updated README and package name

refactor: migrate from cmux to tmux with auto-configuration

Merge pull request #1 from adnbsr/fix/fish-shell-exit-status

fix: use correct exit status variable for fish shell

docs: add README and fix repo URL in package.json

chore: add MIT LICENSE file

test(subagents): add test suite for session and cmux utilities

fix(subagents): improve cmux-not-available error messages

feat(extension): copy session-artifacts extension

feat(subagents): copy extension files and add package agents discovery

chore: scaffold package structure for pi-interactive-subagents