gsd-remove-phase by @shoootyou

<objective> Remove an unstarted future phase from the roadmap and renumber all subsequent phases to maintain a clean, linear sequence.

Purpose: Clean removal of work you've decided not to do, without polluting context with cancelled/deferred markers. Output: Phase deleted, all subsequent phases renumbered, git commit as historical record. </objective>

<execution_context> @{{PLATFORM_ROOT}}/get-shit-done/workflows/remove-phase.md </execution_context>

<context> Phase: $ARGUMENTS

Roadmap and state are resolved in-workflow via init phase-op and targeted reads. </context>

<process> Execute the remove-phase workflow from @{{PLATFORM_ROOT}}/get-shit-done/workflows/remove-phase.md end-to-end. Preserve all validation gates (future phase check, work check), renumbering logic, and commit. </process>