0.2.0: one way to author — Workflow.toLayer hosted by workflowBundle

[bweis]

Prompted by Mattia Manzati's Discord suggestion that a real WorkflowEngine service could retire makeTemporalWorkflow in favor of plain @effect/workflow syntax. It does — fully. This PR makes Workflow.toLayer the only authoring form, hosted by workflowBundle.

What

• workflowBundle(layer) — hosts Workflow.toLayer registrations behind ONE dynamic Temporal default export ("workflow bundle" is Temporal's own name for this artifact — the thing workflowsPath points at). A registration-phase engine collects engine.register calls into a per-V8-context registry (memoized, reuseV8Context-safe, duplicate tags rejected loudly); the default export dispatches by workflow type into the shared per-run wrapper.
• BREAKING: makeTemporalWorkflow is removed. One way to author; the project is young enough to afford the break. If per-type workflowDefinitionOptions (e.g. Worker Versioning behavior) ever becomes a need, the worker-level defaultVersioningBehavior covers the dynamic workflow, and a per-type escape hatch can be reintroduced.
• Layer-provided handler services — registered handlers can require services provided by ordinary Layers composed into the registration environment.

// workflows.ts — the whole bundle entry
export default workflowBundle(
  Layer.mergeAll(OrderFlow.toLayer(orderHandler), BillingFlow.toLayer(billingHandler)),
);

Strictly-better check

• Type safety: the erased handler seam uses a contravariant never payload and the provided-services union for R — no any, exactly one SAFETY-commented cast, replacing the one the old code had at the same spot.
• Coverage: every test fixture bundle (16) and both runnable examples use the bundle form, so the entire feature surface — activities, compensation, mailboxes, updates, state cells, children + attach polling, continue-as-new (re-dispatch through the default export proven end to end), versioning chains, nexus, schedules — exercises the registry path. 57/57 tests green; both examples run in CI.
• Comment diet: constraint comments only; narration and restated-type comments trimmed.
• Docs: the single authoring form taught throughout, no migration-era framing ("plain/upstream syntax" qualifiers removed everywhere). CHANGELOG carries the breaking 0.2.0 entry.

Release after merge: git tag v0.2.0 && git push --tags (trusted publishing).

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