fix(#406): stop ChatView.dom.test leaking a react-virtual timer past teardown

[khaliqgant]

Closes #406.

Problem

ChatView.dom.test.ts intermittently false-reds CI: all tests pass but vitest reports one unhandled error —
ReferenceError: window is not defined from @tanstack/virtual-core Timeout._onTimeout firing after the DOM environment is torn down. Cost a false-red on #401 (green on rerun).

Root cause

@tanstack/virtual-core (observeOffset) registers a scroll handler that, on every scroll event, schedules an isScrolling-reset debounce — targetWindow.setTimeout(() => cb(offset, false), isScrollingResetDelay) (default 150ms). Its unmount cleanup only removeEventListeners the scroll handler; it never clears that pending timeout. The "mounts a different row window after scrolling" test dispatches a scroll near the end, leaving a ~150ms timer queued. If the env teardown wins the race, the callback runs against a torn-down window → the unhandled ReferenceError.

Fix

Drive the suite on fake timers and drop pending timers before restoring real ones:

• beforeEach: vi.useFakeTimers({ shouldAdvanceTime: true }) — the debounce lands in a registry we control; shouldAdvanceTime keeps the clock progressing on real time so RTL waitFor / async act resolve normally.
• afterEach: cleanup() → vi.clearAllTimers() → vi.useRealTimers(). The stray debounce is dropped while the env still exists, closing the race deterministically (no reliance on the timer firing "in time").

Also hardens .gitignore with a node_modules (no trailing slash) entry so a worktree node_modules symlink can't be committed.

Verification

Ran the file 20x consecutively:

=== 20x results: passed=20 failed=0 post-teardown-errors=0 ===

(grep for window is not defined / Unhandled Error / _onTimeout across all 20 runs → none.)
Single-run assertions still pass (2/2), and the run is faster (~848ms vs prior).

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: b009f77d-faae-40a7-b316-7dd67040b9a9

📥 Commits

Reviewing files that changed from the base of the PR and between bea859f and 675c18c.

📒 Files selected for processing (2)

• .gitignore
• src/renderer/src/components/chat/ChatView.dom.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/chatview-virtual-timer-flake

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