chore(hygiene): remove stale pre-#9123 branch comment

Takeaways:
- `src/stores/nodeOutputStore.test.ts:720` says current main is “without PR #9123 guard”.
- [PR #9123](https://github.com/Comfy-Org/ComfyUI_frontend/pull/9123) is merged, so the branch-relative comment is stale on current main.
- Update the comment to describe the behavior/invariant the assertion protects, without a moving-branch claim.

Verification

Audited `origin/main` at `5882b01388fd2d5ef72e00f92e7761ef5f91f3d8`.

Exact location: `src/stores/nodeOutputStore.test.ts:720`.

The test currently says `On current main (without PR #9123 guard), execution overwrites`. GitHub reports PR #9123 merged, while the audited HEAD still contains this text. Searches of open and closed issues/PRs for `PR #9123 nodeOutputStore` found no existing hygiene ticket. The candidate was independently reproduced in a separate fresh clone. Open heads #16373, #16375, #16396, and #16432 do not change this file.

Suggested action: replace the branch-relative sentence with a stable explanation of why execution output replaces the restored input preview in this test, or remove it if the test name and assertions are sufficient.

Open src/stores/nodeOutputStore.test.ts at line 720 and read the surrounding test name and assertions. Replace the branch-relative comment with a stable explanation of the behavior or invariant it protects, or remove it if the test is self-explanatory; done when no stale PR #9123 claim remains.

Written by the indexing model from the issue text.