feat: add cheetah-grid-playwright package

[ota-meshi]

Follow-up to #472. Introduces cheetah-grid-playwright, a new ESM-only workspace package providing official Playwright helpers for driving the grid. Cells are addressed by field name and record index (or raw col/row indices) and operated with real mouse and keyboard events at coordinates computed through the grid API, so interactions go through the same code path as actual user input.

import { gridLocator } from "cheetah-grid-playwright";

const grid = gridLocator(page.locator(".cheetah-grid"));
await grid.cell("email", 3).click();
await grid.cell("email", 3).fill("cat@example.com");
await expect.poll(() => grid.cell("email", 3).value()).toBe("cat@example.com");

The helpers absorb the pitfalls that make hand-written recipes wrong or flaky, found through adversarial review and verified by reproduction:

• Waits for the grid's internal scroll state after makeVisibleCell() (which only moves the DOM scroll position), forcing instant scrolling under scroll-behavior: smooth.
• Scrolls the window (and ancestor frames) to the cell before clicking, clicks the center of the visible part of the cell (cells larger than the grid viewport), and supports grids inside same-origin iframes by converting to top-level viewport coordinates.
• fill() loads lazy records first, opens the editor with F2, waits out the editors' Enter guard, and verifies the commit — failing with the validation message when an inputValidator rejects the value instead of reporting a false success.
• Fails clearly instead of silently misbehaving: out-of-range cells, cells without a text editor (closing an opened menu), multiple grids under one locator, grids scaled by ancestor transforms, cross-origin iframes, and unbuilt fixtures.
• Returns the whole rectangle for merged (colSpan/rowSpan) cells, and never leaks uncaught errors into the page (asserted for every test).

Tests (23) run against local fixture pages with vitest + Playwright (channel: "chrome"), including a smoke test of the built artifact (the page function is serialized at runtime, so the shipped file must be exercised). The lint CI job gains a build phase so type checking can resolve the built cheetah-grid type definitions.

Known limitation, documented in code: the page must expose window.cheetahGrid (the same module instance that created the grid).

This PR also carries two core fixes found through the helper's tests: makeVisibleCell scrolled the start edge of cells larger than the grid viewport out of view on every click, and the resulting scroll closed cell editors right after opening (always in WebKit, in Chrome when horizontally scrolled), making such cells impossible to edit in place; and getCellsRect clamped the row direction of ranges starting in frozen rows by column widths instead of row heights.

Possible follow-ups (not in this PR): menu editors via a selectOption-like API, selection ranges, and event waiting helpers.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 4928b7b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
cheetah-grid	Patch
cheetah-grid-playwright	Minor

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