test: migrate hover, drag and click snapshot tests to mocks - #3192

Please make the following changes:

Keep drags one element onto another as a real-browser test (or add one real-browser drag test) and add only the new mock-based includes snapshot if includeSnapshot is true test in tests/tools/input.test.ts. The drag -> 50 ms sleep -> drop sequence is project logic whose correctness is only observable in a real browser, and #2639 asks to retain a few high-level real-browser tests.

Nits

1. In drags one element onto another, replace the two sinon.assert.calledWith(page.getElementByUid, ...) calls with sinon.assert.calledTwice plus sinon.assert.calledWithExactly(page.getElementByUid.firstCall, '1_1') and secondCall, '1_2', per the "verify exact arguments" rule in AGENTS.md.
2. Use one style for the two drag assertions: sinon.assert.calledOnceWithExactly(toHandle.drop, fromHandle) mirrors the fromHandle.drag assertion and does not need calledOnceWithMatch + sinon.match.same.
3. In the click tests, sinon.assert.calledOnceWithExactly(locator.click, {count: 1, signal: sinon.match.instanceOf(AbortSignal)}) verifies the count argument that the handler derives from dblClick; calledOnce does not.

Please check the following:

1. In tests/tools/input.test.ts › drags › includes snapshot if includeSnapshot is true, replace sinon.assert.calledOnceWithMatch(toHandle.drop, sinon.match.same(fromHandle)) with sinon.assert.calledOnceWithExactly(toHandle.drop, fromHandle). The handler calls toHandle.drop(fromHandle) with one argument, so the exact form matches the fromHandle.drag assertion above it and the "verify exact arguments" rule in AGENTS.md.

2. In tests/tools/input.test.ts › hover › hovers and includes snapshot if includeSnapshot is true, replace sinon.assert.calledOnce(locator.hover) with sinon.assert.calledOnceWithMatch(locator.hover, {signal: sinon.match.instanceOf(AbortSignal)}). The click tests in this PR assert the signal option, and the hover handler passes {signal} the same way.

3. Rename drags › includes snapshot if includeSnapshot is true to describe its full scope (for example calls drag and drop on the element handles and includes snapshot). The name only mentions the snapshot, but the test now holds the only mock-based coverage of the getElementByUid → drag → drop argument forwarding.

4. Update the PR description. After commit 2, the bullet "drags one element onto another: asserts fromHandle.drag and toHandle.drop calls" and the "all 6 migrated tests" count are stale.

Please address the following:

1. In tests/mocks.ts, remove the MockElementHandle intersection type and the handle as unknown as MockElementHandle cast in createMockElementHandle. AGENTS.md forbids the as keyword for type casting, and the cast only exists to make one assertion compile.
2. In tests/tools/input.test.ts (drags › calls drag and drop on the element handles and includes snapshot), restore the commit-2 assertion sinon.assert.calledOnceWithMatch(toHandle.drop, sinon.match.same(fromHandle)). ElementHandle.drop has two overloads and Sinon types the stub with the last (deprecated data?: DragData) one, so sinon.match.same is the type-safe way to check the exact handle without a cast.