Add a published .d.ts diff to the release process to catch breaking type changes

## Problem

4.2.4 shipped as a patch but contained breaking TypeScript type changes with no changelog note. The main one: `ObservableStatus` was refactored from a flat interface (`data: T`) into a discriminated union (`data: T | undefined` unless narrowed on `status`), which breaks the standard destructure-and-use pattern across every data hook, including the documented suspense pattern. It is type-only (no runtime impact), but it reds strict-TS consumer CI on upgrade.

It slipped through because:

- The change came in via #583 ("use `useSyncExternalStore` to sync data"), whose title looked like an internals change, not a public API break.
- It then sat unreleased for ~3 years (v4.2.3 was 2022-08, #583 merged 2023-07).
- 4.2.4 batched 35 PRs of accumulated `main` into one bump, with no step auditing the cumulative public type surface.

## Proposal

Add a release-time (or CI) check that diffs the candidate's emitted types against the last published version:

1. `npm pack` the latest published version, extract `dist/*.d.ts`.
2. `npm pack` the release candidate, extract `dist/*.d.ts`.
3. Diff them. Any non-additive change (removed/narrowed/changed signature) fails the check or requires an explicit "breaking" acknowledgment and a minor/major bump.

This exact diff would have flagged both the `ObservableStatus` union change and the `useFirestoreDocData` widening (#733) immediately.

## Related

- Remediation for the live 4.2.4 release is tracked separately (deprecate + re-cut as 4.3.0 with a migration note).
- Surfaced while reviewing #740.

Start with the repository's existing release or CI process and use npm pack to compare the latest published package with the release candidate. Extract dist/*.d.ts, identify non-additive type changes, and make the check fail or require an explicit breaking acknowledgment with an appropriate version bump.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.