fix(#1871): wire phase archival end-to-end (phases archive cmd + default + atomic) (#1924)

Follow-up to #1919 (archive-then-remove core). Closes the remaining #1871
acceptance criteria so phase history is preserved across the full milestone
lifecycle, not just at phases.clear:

- #2 src/milestone.cts + src/phases-command-router.cts: extract shared
  archivePhaseDirectories() helper; add cmdPhasesArchive (the previously
  half-wired phases.archive alias now routes instead of erroring Unknown).
- #4 gsd-tools.cjs + src/milestone.cts: milestone complete archives phase
  dirs by default (--no-archive-phases opts out; --archive-phases is now a
  harmless no-op). complete-milestone.md updated to drop the redundant manual
  Yes/Skip archive prompt.
- #3 gsd-core/workflows/new-milestone.md: §6 stages the archive move + source
  removal (git add .planning/milestones/ .planning/phases/) in the same commit
  as the milestone start, so the archive lands atomically — no orphaned
  uncommitted deletions, no un-archived dirs inherited.
- docs/CLI-TOOLS.md (+ ja/zh/ko/pt) + help/modes/full.md: flag accuracy.
- tests: phases archive command (#2) + milestone complete default archive /
  --no-archive-phases opt-out (#4). Goldens + workflow size baseline refreshed.

Closes #1871

gsd-core/workflows/complete-milestone.md

@@ -453,21 +453,17 @@ Extract from result: `version`, `date`, `phases`, `plans`, `tasks`, `accomplishm
 
 Verify: `✅ Milestone archived to .planning/milestones/`
 
-**Phase archival (optional):** After archival completes, ask the user:
+**Phase archival (default-on):** `milestone complete` archives phase directories to `milestones/v[X.Y]-phases/` by default (#1871), so the next `/gsd:new-milestone` never inherits un-archived dirs. No manual `mkdir`/`mv` or `--archive-phases` flag is needed.
 
+If the user explicitly wants to keep phase directories in place as raw execution history, invoke `milestone complete` with `--no-archive-phases`:
+
+```bash
+gsd_run query milestone complete v[X.Y] --no-archive-phases
+```
+
+Verify after a default (archived) completion: `✅ Phase directories archived to .planning/milestones/v[X.Y]-phases/`
 
 **Text mode (`workflow.text_mode: true` in config or `--text` flag):** Set `TEXT_MODE=true` if `--text` is present in `$ARGUMENTS` OR `text_mode` from init JSON is `true`. When TEXT_MODE is active, replace every `AskUserQuestion` call with a plain-text numbered list and ask the user to type their choice number. This is required for non-Claude runtimes (OpenAI Codex, Gemini CLI, etc.) where `AskUserQuestion` is not available.
-AskUserQuestion(header="Archive Phases", question="Archive phase directories to milestones/?", options: "Yes — move to milestones/v[X.Y]-phases/" | "Skip — keep phases in place")
-
-If "Yes": move phase directories to the milestone archive:
-```bash
-mkdir -p .planning/milestones/v[X.Y]-phases
-# For each phase directory in .planning/phases/:
-mv .planning/phases/{phase-dir} .planning/milestones/v[X.Y]-phases/
-```
-Verify: `✅ Phase directories archived to .planning/milestones/v[X.Y]-phases/`
-
-If "Skip": Phase directories remain in `.planning/phases/` as raw execution history. Use `/gsd:cleanup` later to archive retroactively.
 
 After archival, the AI still handles:
 - Reorganizing ROADMAP.md with milestone grouping (requires judgment) — overwrite in place after extracting Backlog section