fix: use direct git merge for master, worktree only for epic branches

fix: sort children by ID ascending in epic/issue detail view

perf: parallelize child ID collection in list_issues

feat: replace c/p copy keys with vim-style yi/yp yank operations

refactor: replace q key quit with Ctrl-C

fix: add -f flag to worktree add in merge_into_branch

refactor: replace ChildDetail with navigation stack, support nested epics

refactor: update list_issues to exclude child issues from results

docs: add TopLevel/Standalone/Child issue taxonomy to ubiquitous language

docs: rewrite README, add CLAUDE.md, remove SPEC.md

refactor: add ConfirmAction::label() to deduplicate keybar match

refactor: simplify merge_epic_to_master to use merge_into_branch

refactor: add page_ and ai_ prefixes to feature module directories

refactor: extract clipboard operations into clipboard/ module

refactor: convert editor.rs to editor/ directory module