Clean up dead demos and restructure directory layout

Phase 1 - Remove dead/duplicate content:
- Delete demos/samples_java/ (incomplete Java demo)
- Delete demos/shared/chatbot_ui/ (replaced by AnythingLLM)
- Delete demos/shared/grafana/, prometheus/, logfire/, honeycomb/, signoz/
  (legacy observability stacks; only jaeger is retained)
- Delete variant docker-compose files (honeycomb, logfire, signoz, jaeger)
- Delete demos/use_cases/spotify_bearer_auth/run_demo.sh (stale script)

Phase 2 - Restructure into semantic categories:
- getting_started/  : weather_forecast, llm_gateway
- agent_orchestration/ : travel_agents, multi_agent_crewai_langchain
- llm_routing/       : model_alias_routing, preference_based_routing, claude_code_router
- filter_chains/     : http_filter, mcp_filter
- integrations/      : ollama, spotify_bearer_auth
- advanced/          : model_choice_test_harness, multi_turn_rag,
                       currency_exchange, stock_quote

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

demos/samples_python/multi_turn_rag_agent/Dockerfile

@@ -1,19 +0,0 @@
-FROM python:3.12 AS base
-
-FROM base AS builder
-
-WORKDIR /src
-
-COPY requirements.txt /src/
-RUN pip install --prefix=/runtime --force-reinstall -r requirements.txt
-
-COPY . /src
-
-FROM python:3.12-slim AS output
-
-COPY --from=builder /runtime /usr/local
-
-COPY . /app
-WORKDIR /app
-
-CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "80", "--log-level", "info"]