refactor(pm): clean up pm integration layer

[zbigniewsobiecki]

Summary

Post-refactoring cleanup of the PM integration subsystem.
Removes dead code, improves type safety, eliminates
duplication, and consolidates lifecycle config into a
single source of truth.

• Remove unused getTriggerHandlers() from PMIntegration
  interface and both implementations
• Remove unused withCredentials() from registry
• Change createProvider() to accept ProjectConfig
  directly (eliminates unsafe PMProviderConfig casts)
• Change TriggerResult.agentType from string to
  string | null (explicit nullability)
• Delete factory.ts (inline into index.ts)
• Delegate ack/reaction methods in Trello and JIRA
  integrations to existing router functions (~200 lines
  of duplicated code removed)
• Consolidate resolveLifecycleConfig — integration
  implementations become single source of truth
• Replace redundant createPMProvider() calls with
  getPMProvider() in webhook-handler
• Migrate TriggerResult.cardId to workItemId across
  all 14 trigger files and 2 consumers

73 files changed, +1174 / -1809 lines

Test plan

• All 155 test files pass (2489 tests)
• TypeScript compiles with zero errors
• ESLint passes with zero warnings
• Pre-push hook passes (lint + typecheck + tests)
• Updated test mocks for PM registry side-effect
  imports where needed

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