refactor: new timeline component

- Create new timeline component (extracted from asset-gird) without removing old code
- Add timeline/, timeline/actions/, timeline/base-components/, and timeline/internal-components/ directories
- Copy needed components (delete-asset-dialog, scrubber, skeleton) to new locations
- Add new timeline components (base-timeline, base-timeline-viewer, timeline-month, etc.)
- Update timeline-util.ts with new functions (findMonthAtScrollPosition, formatGroupTitleFull)
- Add asset-viewer-actions and asset-viewer-and-actions components

This allows the timeline to exist alongside the current AssetGrid component.

web/src/lib/managers/timeline-manager/timeline-manager.svelte.ts

@@ -41,6 +41,7 @@ export class TimelineManager {
   isInitialized = $state(false);
   months: MonthGroup[] = $state([]);
   topSectionHeight = $state(0);
+  bottomSectionHeight = $state(60);
   timelineHeight = $derived(this.months.reduce((accumulator, b) => accumulator + b.height, 0) + this.topSectionHeight);
   assetCount = $derived(this.months.reduce((accumulator, b) => accumulator + b.assetsCount, 0));
 
@@ -552,4 +553,13 @@ export class TimelineManager {
   getAssetOrder() {
     return this.#options.order ?? AssetOrder.Desc;
   }
+
+  getMaxScrollPercent() {
+    const totalHeight = this.timelineHeight + this.bottomSectionHeight + this.topSectionHeight;
+    return (totalHeight - this.viewportHeight) / totalHeight;
+  }
+
+  getMaxScroll() {
+    return this.topSectionHeight + this.bottomSectionHeight + (this.timelineHeight - this.viewportHeight);
+  }
 }