Refactor TimelineCanvas.onTimelineDataLoad to use waitForDomRect

The current implementation of onTimelineDataLoad in TimelineCanvas.mjs uses a recursive retry logic with setTimeout to wait for DOM elements (ticket avatars/badges) to be available. This mimics the behavior of waitForDomRect, but in an ad-hoc, less robust way.

We should refactor this method to be async and explicitly use waitForDomRect for the target elements. This will simplify the code, leverage the framework's built-in robust waiting mechanism, and ensure consistent behavior.

Proposed Change:

1. Make onTimelineDataLoad async.
2. Replace the me.timeout(delay).then(...) and the retry logic with a call to me.waitForDomRect({ id: ids, attempts: 20, delay: 50 }).
3. Handle the case where waitForDomRect returns valid rects directly.

Current Logic:

        // If this is a fresh data load (not a resize), wait a bit for DOM
        let delay = attempt === 0 ? 0 : 50;

        me.timeout(delay).then(async () => {
            // ... fetch rects
            // ... retry if missing
        });

New Logic (Conceptual):

    async onTimelineDataLoad(records, isResize = false) {
        // ... (guards)
        let ids = records.map(r => `${r.id}-target`);
        let rects = await me.waitForDomRect({ id: ids, attempts: 20, delay: 50 });
        // ... (process rects)
    }

This change aligns TimelineCanvas with the robust pattern used elsewhere (e.g., in MainContainerController).