cmdInitPlanPhase, cmdInitExecutePhase, and cmdInitVerifyWork returned
phase_found: false when the phase existed in ROADMAP.md but no phase
directory had been created yet. This caused workflows to fail silently
after /gsd:new-project, producing directories named null-null.
cmdInitPhaseOp (used by discuss-phase) already had a ROADMAP fallback.
Applied the same pattern to the three missing commands: when
findPhaseInternal returns null, fall back to getRoadmapPhaseInternal
and construct phaseInfo from the ROADMAP entry.
Added 5 regression tests covering:
- plan-phase ROADMAP fallback
- execute-phase ROADMAP fallback
- verify-work ROADMAP fallback
- phase_found false when neither directory nor ROADMAP entry exists
- disk directory preferred over ROADMAP fallback
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