End-to-end feature implementation pipeline for a GitHub issue. Creates a git worktree, explores the codebase, plans, delegates implementation to the bundled `@developer` agent, runs review via the bundled `@reviewer` agent, and opens a pull request. Use when the user says "implement task", "implement issue #N", "implement <feature>", invokes `/implement-task`, or asks to implement a GitHub issue end-to-end.
