Story 2011: real Vega invoke

This removes the last no-op in the Matter Brief chain. A matter.created event now claims the frame job, invokes Vega's AgentCore runtime, consumes the terminal stream, and writes the returned FrameOutput through the existing Story-1996 ingest boundary.

What changed

Surface	Change
`framer_trigger.handler`	Replaces the logging stub with `bedrock-agentcore.invoke_agent_runtime` against `AGENT_RUNTIME_ARN_FRAMER`, using `text/event-stream`.
`framer_trigger.processor`	Assembles Vega's real `FramerInput`, marks the run `running`, ingests the terminal frame, and stamps `succeeded` or `failed`.
`MatterFrameService.ingest_agent_frame`	Remains the only write path: validates `FrameOutput`, overlays locks, honors generation CAS, appends `business.matter_frames`, audits, and emits `matter_frame.updated`.

Execution chain

matter.created
  -> framer_trigger firm-scoped claim
  -> agents.agent_run status=running
  -> InvokeAgentRuntime(AGENT_RUNTIME_ARN_FRAMER)
  -> Vega agent_event_stream.v1 turn.completed(frame)
  -> MatterFrameService.ingest_agent_frame
  -> business.matter_frames row
  -> agents.agent_run status=succeeded

Verification

uv run pytest tests/unit/test_framer_trigger_processor.py tests/unit/test_framer_trigger_handler.py -q
uv run ruff check src/workers/framer_trigger/handler.py src/workers/framer_trigger/processor.py src/shared/settings.py tests/unit/test_framer_trigger_handler.py tests/unit/test_framer_trigger_processor.py tests/integration/test_framer_trigger_jobs.py
uv run mypy --follow-imports=skip src/workers/framer_trigger/handler.py src/workers/framer_trigger/processor.py
set -a; . ./.env.test-db; set +a; uv run pytest tests/integration/test_framer_trigger_jobs.py -q

Deployment note: after merge, run deploy-framer-trigger.yml so the stale framer-trigger Lambda artifact receives this invoke code.