fix(agents): enforce Sisyphus->Hephaestus->Prometheus->Atlas assembly order

Extract hephaestus into agentConfig before prometheus so the config
handler naturally assembles agents in the canonical order instead of
relying solely on reorderAgentsByPriority to fix the wrong intermediate
order. Also fix test data that had atlas/prometheus swapped and add
missing hephaestus to agent-config-integration test lists.

src/plugin-handlers/config-handler.test.ts

@@ -1205,8 +1205,8 @@ describe("per-agent todowrite/todoread deny when task_system enabled", () => {
   const AGENTS_WITH_TODO_DENY = new Set([
     getAgentListDisplayName("sisyphus"),
     getAgentListDisplayName("hephaestus"),
-    getAgentListDisplayName("atlas"),
     getAgentListDisplayName("prometheus"),
+    getAgentListDisplayName("atlas"),
     getAgentListDisplayName("sisyphus-junior"),
   ])
 
@@ -1218,8 +1218,8 @@ describe("per-agent todowrite/todoread deny when task_system enabled", () => {
     createBuiltinAgentsMock.mockResolvedValue({
       sisyphus: { name: "sisyphus", prompt: "test", mode: "primary" },
       hephaestus: { name: "hephaestus", prompt: "test", mode: "primary" },
-      atlas: { name: "atlas", prompt: "test", mode: "primary" },
       prometheus: { name: "prometheus", prompt: "test", mode: "primary" },
+      atlas: { name: "atlas", prompt: "test", mode: "primary" },
       "sisyphus-junior": { name: "sisyphus-junior", prompt: "test", mode: "subagent" },
       oracle: { name: "oracle", prompt: "test", mode: "subagent" },
     })