test: add dedicated integration tests for 12 orchestration crates (#141)

Add 175 integration tests across all 12 orchestration crates that
previously only had inline unit tests:

- warpgrid-raft (6 tests): log store lifecycle, snapshot roundtrip,
  membership persistence, concurrent reader/writer safety
- warpgrid-cluster (5 tests): join/leave lifecycle, heartbeat updates,
  dead node detection, concurrent join safety, TLS cert validation
- warpgrid-rollout (13 tests): rolling/canary/blue-green lifecycles,
  rollback, pause/resume, serialization roundtrip
- warpgrid-placement (11 tests): heterogeneous placement, affinity
  labels, preemption, scoring weight effects
- warpgrid-autoscale (15 tests): mixed scale decisions, scale-to-zero,
  cooldown, latency/memory-based scaling
- warpgrid-scheduler (18 tests): round-robin balancer, placement
  executor, distributed placement, lifecycle errors
- warpgrid-health (12 tests): HTTP probes, state transitions,
  monitor lifecycle, exponential backoff, timeout handling
- warpgrid-metrics (14 tests): collector lifecycle, snapshot resets,
  Prometheus exposition, percentile accuracy, auto-discover
- warpgrid-proxy (24 tests): state sync, unhealthy backend skip,
  DNS namespaces, TLS wildcard matching, event-driven updates
- warpgrid-api (13 tests): CRUD lifecycle, rollout API, scale
  validation, Prometheus endpoint, response format consistency
- warpgrid-trigger (14 tests): echo handler, concurrent requests,
  header roundtrip, URI edge cases, status boundaries
- warpgrid-dashboard (30 tests): page rendering, scale actions,
  density demo, view helper edge cases

All tests use in-memory backends and ephemeral ports — no external
services required. Closes #141.

Author: nadilas

Cargo.lock

@@ -15,3 +15,7 @@ tokio.workspace = true
 tracing.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+
+[dev-dependencies]
+tower = { version = "0.5", features = ["util"] }
+http-body-util = "0.1"