[use-effect] Replace reset-on-prop Effect with render-time state adjustment in Chip

## Effect location and classification

`Chip` in `packages/editor/src/changes-chip.tsx` (the `PlanChanges` per-edge indicator) had:

```ts useEffect(() => { if (waiting === 0) setOpen(false); }, [waiting]); ```

This is a `reset-or-adjust-state` Effect: it only reacts to the `waiting` prop crossing to `0` and forces `open` back to `false`. It does not synchronize with any external system (no DOM API, network, subscription, or store) — it exists purely to keep one piece of state consistent with another.

## Why it was incorrect

Per the "you don't need an Effect" guidance, adjusting state in response to a prop change inside a Effect causes an extra render: React first commits with the stale `open` value (the list still open for a `waiting === 0` frame), the Effect then runs, calls `setOpen(false)`, and a second render/commit happens. This produces a visible flash of an open, now-empty change list before it closes, and adds an unnecessary render pass.

## Refactor

Replaced the Effect with React's documented "adjusting state during render" pattern: track the `waiting` value the `open` state was last computed for (`openedForWaiting`), and when `waiting` changes, call `setOpen(false)` synchronously in the render body (before returning JSX) rather than in a Effect. React detects the state update during render and re-renders immediately with the corrected value in the same commit, avoiding the stale intermediate frame. The existing outside-click-to-close Effect (a legitimate `external-sync` Effect for a `document` event listener) was left untouched.

## Verification

`bun`, `dprint`, and `oxlint` were not available in this sandboxed environment (no network access to fetch the Bun binary or install the workspace's pinned toolchain), so `bun test` / `bun run types` / `bun run ci` could not be executed. I verified the change by: - Manual review against React's documented state-adjustment-during-render pattern. - Confirming the file's existing tab/quote/semicolon formatting conventions are preserved. - Tracing all call sites of `open`/`setOpen` in the component to confirm no other logic depends on the Effect timing.

Given the tooling limitation, please run `bun run types` (or the editor package's narrower check) and `bun run ci` locally before merging to confirm formatting and type-correctness.

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githubnext/chopinPublic

[use-effect] Replace reset-on-prop Effect with render-time state adjustment in Chip #126