fix(agents): include SOUL.md, IDENTITY.md, USER.md in subagent/cron bootstrap allowlist

Subagent and isolated cron sessions only loaded AGENTS.md and TOOLS.md,
causing subagents to lose their role personality, identity, and user
preferences. Expand MINIMAL_BOOTSTRAP_ALLOWLIST to include the three
missing identity files.

Closes #24852

(cherry picked from commit c33377150e)

src/hooks/bundled/bootstrap-extra-files/handler.test.ts

@@ -92,7 +92,10 @@ describe("bootstrap-extra-files hook", () => {
 
     const event = createHookEvent("agent", "bootstrap", "agent:main:subagent:abc", context);
     await handler(event);
-
-    expect(context.bootstrapFiles.map((f) => f.name).toSorted()).toEqual(["AGENTS.md", "TOOLS.md"]);
+    expect(context.bootstrapFiles.map((f) => f.name).toSorted()).toEqual([
+      "AGENTS.md",
+      "SOUL.md",
+      "TOOLS.md",
+    ]);
   });
 });