fix(#4078): phase.complete next-phase cascade reads dash-grammar checkbox rows (#4301)

* test(#4078): phase.complete mixed-grammar roadmap picks lowest outstanding phase, not positional-last

* fix(#4078): accept dash-grammar checkbox rows in phase.complete next-phase cascade

Stage 2 (roadmap identity scan) and stage 3 (#2028 lowest-outstanding
override) required a colon separator after the phase number, while the
canonical phase lookup has accepted the bullet-house dash grammar
(- [ ] **Phase N — Name**, #2199) for years. On a mixed-grammar roadmap
the only parseable row above N was a later phase.add-ingested colon-form
phase - positionally last - and it won the numeric-minimum vote it should
never have been alone in: completing Phase 1 of 18 selected Phase 18 and
skipped phases 2-17 (#4078).

The checkbox branches now accept the #2199 separator class (em/en-dash,
hyphen, colon); heading branches stay colon-only, mirroring
findRoadmapPhaseInContent exactly.

* test(#4078): align regression fixtures with slug name + checked-box semantics

* fix(#4078): drop unnecessary type assertion flagged by eslint

* chore(#4078): add changeset fragment

* chore(#4078): backfill PR number in changeset

---------

Co-authored-by: sim <sim@local>

.changeset/nimble-quails-climb.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4301
+---
+**`phase.complete` no longer skips to the positionally-last phase on mixed-grammar roadmaps** — completing a phase now advances to the lowest outstanding phase even when the roadmap's rows use the dash form (`- [ ] **Phase N — Name**`); previously only colon-form rows were visible to next-phase selection, so a later phase.add-ingested phase could win and jump `current_phase` seventeen phases ahead. (#4078)