gsd-plan-phase

<objective> Create executable phase prompts (PLAN.md files) for a roadmap phase with integrated research and verification. **Default flow:** Research (if needed) → Plan → Verify → Done **Research-only mode (`--research-phase <N>`):** Spawn `gsd-phase-researcher` for phase `N`, write `RESEARCH.md`, then exit before the planner runs. Useful for cross-phase research, doc review before committing to a planning approach, and correction-without-replanning loops where iterating on research alone is dramatically cheaper than re-spawning the planner. Replaces the deleted research-phase command (#3042). **Research-only modifiers:** - **No flag** — when `RESEARCH.md` already exists, auto-uses it: emits a one-line notice and exits cleanly, no prompt. - **`--research`** — force-refresh: re-spawn the researcher unconditionally, no prompt. Bypasses the existing-RESEARCH.md auto-use path. - **`--view`** — view-only: print existing `RESEARCH.md` to stdout. Does not spawn the researcher. Cheapest mode for the correction-without-replanning loop. If no `RESEARCH.md` exists yet, errors with a hint to drop `--view`. **Orchestrator role:** Parse arguments, validate phase, research domain (unless skipped), spawn gsd-planner, verify with gsd-plan-checker, iterate until pass or max iterations, present results. </objective> <execution_context> @~/.claude/gsd-core/workflows/plan-phase.md @~/.claude/gsd-core/references/ui-brand.md </execution_context> <runtime_note> **Copilot (VS Code):** Use `vsco...