Retire the smoke-10 chaos scenario; convergence is covered in-process

smoke-10 was a no-stressor 10-node tree-convergence sanity check (netem
off, no ping). Its subject, spanning-tree convergence and root election,
is now covered in-process, faster and deterministically, by the loopback
spanning-tree harness (src/node/tests/spanning_tree.rs: ring, star,
chain, 100-node and disconnected-component convergence) plus end-to-end
datagram delivery (src/node/tests/forwarding.rs). Real-UDP convergence
smoke still runs via static-mesh and the other scenarios' baseline
assertions, so no Docker coverage is lost.

Drop it from both runners in lockstep (the CHAOS_SUITES list and the
GitHub chaos matrix) so the parity guard stays green, delete the scenario
YAML, and update the chaos README.

testing/chaos/README.md

@@ -18,7 +18,7 @@ Ethernet). Logs are collected and analyzed automatically.
 
 ```bash
 ./testing/chaos/scripts/build.sh
-./testing/chaos/scripts/chaos.sh smoke-10
+./testing/chaos/scripts/chaos.sh churn-mixed
 ```
 
 ## Available Scenarios
@@ -29,12 +29,10 @@ Random topologies with increasing stressor intensity.
 
 | Scenario | Nodes | Topology         | Duration | Netem | Link Flaps | Traffic | Node Churn | Bandwidth |
 | -------- | ----- | ---------------- | -------- | ----- | ---------- | ------- | ---------- | --------- |
-| smoke-10 | 10    | random_geometric | 60s      | --    | --         | --      | --         | --        |
 | chaos-10 | 10    | random_geometric | 120s     | yes   | yes        | yes     | --         | --        |
 | churn-10 | 10    | random_geometric | 600s     | yes   | yes        | yes     | yes        | --        |
 | churn-20 | 20    | erdos_renyi      | 600s     | yes   | yes        | yes     | yes        | yes       |
 
-- **smoke-10**: Baseline sanity check. No stressors, just verify tree convergence.
 - **chaos-10**: Network degradation (5-50ms delay, 0-2% loss), link flaps (max 2
   down, 10-30s), and iperf traffic (max 3 concurrent). Netem mutates 30% of
   links every 15-30s between normal and degraded policies.

testing/chaos/scenarios/smoke-10.yaml

@@ -1,51 +0,0 @@
-scenario:
-  name: "smoke-10"
-  seed: 42
-  duration_secs: 30
-
-topology:
-  num_nodes: 10
-  algorithm: random_geometric
-  params:
-    radius: 0.5
-  ensure_connected: true
-  subnet: "172.20.0.0/24"
-  ip_start: 10
-  # The one scenario that deliberately does NOT pin the root. Every other
-  # scenario assigns identities in NodeAddr order so that n01 is root and its
-  # diagram describes the tree that actually forms. That is right for them,
-  # because they test parent selection and were silently testing it under a
-  # root they did not intend, but applying it everywhere would leave root
-  # election itself exercised nowhere. This is the generic 10-node convergence
-  # baseline and its `baseline` assertion is root-agnostic, so it is the
-  # cheapest place to keep election under test.
-  # Do not "fix" this to true for consistency with the others.
-  pin_root: false
-
-# Phase 2+ features (disabled for MVP)
-netem:
-  enabled: false
-
-link_flaps:
-  enabled: false
-
-traffic:
-  enabled: false
-
-# Baseline: the mesh came up, agreed on a root, and took parents. This
-# asserts nothing about any particular subsystem; it exists so that a
-# run in which the mesh never formed cannot report success, which until
-# now it could, because this scenario carried no assertions at all.
-#
-# Ten nodes, one root, nine parented in all six provably-completed
-# archived runs. As the smoke test this is the scenario whose silent
-# success was least defensible.
-assertions:
-  baseline:
-    min_nodes_reporting: 10
-    max_roots: 1
-    min_nodes_parented: 9
-
-logging:
-  rust_log: "info"
-  output_dir: "./sim-results"