feat: casehub-examples/ — working examples module ported from casehub-poc (blocks poc archival)

[mdproctor]

The casehub-examples/ module does not yet exist in casehub-engine. It is a prerequisite for archiving the casehub-poc repo.

Scope

Port and update the following examples from casehub-poc to the casehub-engine API (Binding, Worker, CaseDefinition, CaseContext, etc.):

• DocumentAnalysisApp — basic case with multiple workers, entry criteria, CaseFile state
• LlmReasoningWorker / LlmAnalysisTaskDefinition / DocumentAnalysisWithLlmApp — LLM-backed worker using the Worker SPI
• StageBasedDocumentProcessingExample — stage lifecycle, exit criteria, autocomplete
• StageBasedWorkerIntegrationExample — stages + worker integration
• Signal-based autonomous monitoring — replacement for AutonomousMonitoringWorker; demonstrates the Signal mechanism that supersedes notifyAutonomousWork()

Notes

• Examples depend on casehub-quarkus/ for CDI wiring — coordinate with epic: casehub-quarkus/ — Quarkus extension module (CDI integration, @CaseType, TaskDefinition sugar, Dev Services) #235
• Use casehub-persistence-memory for all examples (no database required)
• The casehub-poc repo can be archived once these examples exist and are demonstrably working

Refs casehub-poc migration plan: docs/superpowers/specs/2026-04-14-casehub-engine-migration-plan.md