Replace direct cross-phase handler calls with orchestrator dispatch loop

[VincentShipsIt]

Parent: #126

What

Replace 14+ direct handlers.startX() cross-calls with a return-value dispatch pattern. Each phase handler returns a typed outcome instead of calling the next phase:

type PhaseOutcome =
  | { next: 'review'; plan: ShipCodePlan }
  | { next: 'execute'; plan: ShipCodePlan }
  | { next: 'testing' }
  | { next: 'verification' }
  | { next: 'commit' }
  | { next: 'shipping' }
  | { next: 'plan'; prompt: string }
  | { next: 'failed'; error: string }
  | { next: 'awaiting_approval' }
  | { next: 'retry'; delayMs: number; target: PhaseOutcome['next'] };

Orchestrator loop receives the outcome and dispatches the next phase. Explicit state machine replaces implicit call graph.

Scope

• packages/pipeline/src/pipeline/shared.ts — PhaseOutcome type, remove PipelinePhaseHandlers
• packages/pipeline/src/pipeline/planning-phases.ts — return outcomes instead of calling handlers
• packages/pipeline/src/pipeline/execution-phases.ts — return outcomes instead of calling handlers
• packages/pipeline/src/pipeline.ts — new dispatch loop

Estimate

~400 lines. Highest risk item — restructures control flow across the entire pipeline. Needs comprehensive test coverage before and after.

Depends on

#131 (split context) should land first so the dispatch loop operates on clean types.