Fix/ag UI full int

[gitsad]

What does this PR do?

Extends the @mobile-reality/mdma-agui bridge from "render streamed MDMA" into a full AG-UI
integration: out-of-band document delivery (CUSTOM events), an agentic activity feed,
interrupt-based resume, and shared-state hydration. Adds a runnable end-to-end example
(OpenRouter backend + React frontend) and updates the AG-UI docs section.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing behavior to change)
  — resumeMode defaults to 'auto': a user decision now resolves a matching AG-UI interrupt
  instead of always opening a fresh user turn. Pass resumeMode: 'user-turn' to restore.
• Refactor (no functional change)
• Documentation
• CI / tooling

Packages Affected

• @mobile-reality/mdma-agui
• @mobile-reality/mdma-spec
• @mobile-reality/mdma-parser
• @mobile-reality/mdma-runtime
• @mobile-reality/mdma-attachables-core
• @mobile-reality/mdma-renderer-react
• @mobile-reality/mdma-prompt-pack
• Blueprint: ___________

Checklist

• I have read the CONTRIBUTING guide.
• My code follows the existing code style (pnpm format and pnpm lint pass).
• I have added or updated tests that cover my changes.
• All tests pass (pnpm test) — 36/36 in mdma-agui.
• Type-checking passes (pnpm typecheck).
• I have added a changeset — 4 changesets, all minor → mdma-agui 0.2.0 → 0.3.0.

How to Test

1. cd examples/integrations/ag-ui && cp .env.example .env — add an OPENROUTER_API_KEY.
2. pnpm backend (→ :8787) and pnpm dev (→ :5188) in two terminals.
3. Hit ▶ Play demo to replay a scripted bug-report conversation, or try it by hand:
   the agent renders a form, fills it from your description, and "set severity to high"
   updates that one field in place — no duplicate form.
4. pnpm verify — asserts value changes route to set_state with zero re-renders, while
   structural changes ("add a phone field") still re-render via generate_mdma.