runtime: fold venue adapters into the restart and poison sweeps

[mfw78]

What

Fold venue adapters (providers) into the supervisor's restart and poison-recovery sweeps, alongside modules. A trap in a routed adapter call marks a shared Liveness dead; the sweep restarts the provider through the module backoff policy and quarantines a crash-looper through the poison policy. A dead venue now resolves to Unavailable, distinct from UnknownVenue, and adapter_alive_count tracks live routability. Adds the flaky-venue fixture, whose submit traps on a poison chain-head sentinel and recovers once the head moves on, to drive the trap-to-recovery and poison paths end to end.

Why

Adapters currently boot once and install but sit outside the sweeps, so a trapped adapter stays dead until the process restarts, and the router can only project the trap to an internal error. Folding adapters into the sweeps recovers them automatically and lets a strategy tell an unknown venue apart from a temporarily dead one.

Closes #378

Testing

• dead_venue_is_unavailable_not_unknown, a_dead_incumbent_is_replaced_on_reinstall in host/venue_registry.rs.
• e2e_trapped_adapter_is_swept_and_restarts, e2e_crash_looping_adapter_is_poisoned in supervisor/tests.rs, over the new flaky-venue wasm fixture.
• cargo fmt --all --check, cargo check --workspace --all-features, cargo clippy --workspace --all-targets --all-features -- -D warnings, cargo nextest run --workspace --all-features, cargo test --doc.

AI Assistance

Implemented with Claude Code under review.