M9 — Middleware (aiohttp + OTel) + host examples

[nficano]

Goal

Middleware (aiohttp + OTel) + host examples.

Scope

• Add src/arcp/middleware/aiohttp.py (arcp_aiohttp_handler + serve_arcp_aiohttp)
• Add src/arcp/middleware/otel.py (with_tracing(inner, *, tracer) per Phase 5 §1.3, with v1.1 span attrs arcp.lease.expires_at / arcp.budget.remaining)
• Examples: host_asgi/, host_aiohttp/, host_tracing/

Spec §

§4.1, §11

Risk

L