feat: shared event-UI conformance harness (event-ui-conformance-harness)

[enricopiovesan]

Summary

• Add language-agnostic fixture catalog under fixtures/event-ui-conformance/ (happy / error / blocked / ended / multi-capability / replay).
• Add workspace package packages/event-ui-conformance with pure mapPresentationState and mapCapabilityProgress helpers + Vitest coverage.
• Document consumer import path in docs/event-ui-conformance-harness.md.

Governing Spec

• docs/specs/001-ui-event-state-conformance/spec.md
• docs/specs/002-capability-event-ui-subscription/spec.md
• ADR docs/adr/0001-event-fixture-harness-first.md
• Public API: embedder event envelope (state_changed | capability_invoked | capability_result | error)

Project Item

• Ticket ID: event-ui-conformance-harness
• Project 2 item: PVTI_lADOEbiBt84BbzAzzg2JmO0

Definition of Done

• Shared fixture catalog covering happy / error / blocked / ended / multi-capability / replay
• Pure mapper for idle|loading|loaded|blocked|ended|error
• Capability-progress helper asserting invoke/result order
• Unit tests green for harness package
• Consumer doc (docs/event-ui-conformance-harness.md)
• No production app emits fake embedder events (harness is test/helper-only)

Validation

• npm run test -w event-ui-conformance
• npm run typecheck -w event-ui-conformance
• npm run lint -w event-ui-conformance
• npm run test / npm run typecheck / npm run lint (all workspaces)
• Fixtures are static JSON (no network)

Production-baseline (N/A)

Docs/helpers-only foundational harness; no platform embedder shipping path change in this PR. Per-app apply tickets will wire hosts later.

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