Fix Codex image generation tool timeout (#84369)

Summary:
- The branch gives Codex `image_generate` dynamic-tool calls a 120s default watchdog in main and side-thread paths and updates docs, tests, and changelog.
- Reproducibility: yes. Source inspection on current main shows unconfigured Codex `image_generate` calls fall ... -tool default, and the linked source PR includes live Gateway before/after output for the timeout behavior.

Automerge notes:
- PR branch already contained follow-up commit before automerge: fix(clawsweeper): address review for automerge-openclaw-openclaw-8425…
- PR branch already contained follow-up commit before automerge: Fix Codex image generation tool timeout

Validation:
- ClawSweeper review passed for head 10c7f87023.
- Required merge gates passed before the squash merge.

Prepared head SHA: 10c7f87023
Review: https://github.com/openclaw/openclaw/pull/84369#issuecomment-4493288493

Co-authored-by: clawsweeper <274271284+clawsweeper[bot]@users.noreply.github.com>
Co-authored-by: moritzmmayerhofer <254141390+moritzmmayerhofer@users.noreply.github.com>
Co-authored-by: clawsweeper[bot] <274271284+clawsweeper[bot]@users.noreply.github.com>
Approved-by: takhoffman
Co-authored-by: takhoffman <781889+takhoffman@users.noreply.github.com>

docs/plugins/codex-harness-reference.md

@@ -256,6 +256,8 @@ available timeout in this order:
 
 - A positive per-call `timeoutMs` argument.
 - For `image_generate`, `agents.defaults.imageGenerationModel.timeoutMs`.
+- For `image_generate` without a configured timeout, the 120 second
+  image-generation default.
 - For the media-understanding `image` tool, `tools.media.image.timeoutSeconds`
   converted to milliseconds, or the 60 second media default.
 - The 30 second dynamic-tool default.