test(snapshot): tighten todo_write item schema in master's new acp snapshots

The origin/master merge added the session-query-spill and
escalation-approved acp scenarios, whose pinned tool-schemas still
carried additionalProperties: true on the todo_write item schema. This
PR tightens that to false (model-visible via the request header), so
re-record it in the two new expected outputs. session-sandbox-root,
escalation-rejected, and fs-escalation-approved compare against the
escalation-approved pinned header and pass once it is fixed.

examples/acp-agent/tests/snapshots/escalation-approved/tool-schemas.expected.json

@@ -288,7 +288,7 @@
             "description": "The COMPLETE task list, replacing any previous list.",
             "items": {
               "type": "object",
-              "additionalProperties": true,
+              "additionalProperties": false,
               "properties": {
                 "content": {
                   "type": "string",

examples/acp-agent/tests/snapshots/session-query-spill/tool-schemas.expected.json

@@ -492,7 +492,7 @@
             "description": "The COMPLETE task list, replacing any previous list.",
             "items": {
               "type": "object",
-              "additionalProperties": true,
+              "additionalProperties": false,
               "properties": {
                 "content": {
                   "type": "string",