fix(library) - Do The Alphabet Dance

[mattsigal]

Pull Request

Summary

Resolves the two-press requirement when performing an alphabetical quick jump in library screens, and optimizes cold-start letter scanning performance by chunking prefix page fetches.

Related Issues

Link related issues or tickets separated by commas.

• Closes #
• Fixes #
• Related to #

Type of Change

• Bug fix
• New feature
• Refactor
• Performance improvement
• UI/UX update
• Documentation update
• Build/CI change
• Other (describe):

Changes Made

List the key changes included in this PR.

• library_browse_screen.dart: Implemented a multi-frame scroll convergence loop in _jumpToLetter to iteratively jump and settle frame layouts until targetOffset is reached, ensuring maxScrollExtent lazy sliver expansion completes in 1-3 frames before requesting item focus.
• library_browse_view_model.dart: Added optional pageSizeOverride parameter to loadMore and _fetchPage, and configured ensureItemsLoadedForPrefix to fetch in 300-item page chunks instead of 48-item pages during letter scans (reducing cold-start prefix scan times from ~30s to <1.5s).

Platform

• Android
• iOS
• tvOS
• Web
• macOS
• Windows
• Linux
• All / Shared code

Testing

Describe how this change was tested.

• Tested on emulator / simulator
• Tested on physical device
• Manual testing completed
• Not tested (explain why):

Test Steps

1. Open any library screen (Movies, TV Shows, Audio, etc.) with a large number of items.
2. Select any letter on the Alphabet quick jump bar.
3. Verify that the grid scrolls directly to the target letter row and focuses the first item in 1 single press.
4. Verify on a fresh install / cold boot that jumping to letters far down the alphabet (e.g. T, W, Z) completes in ~1 second instead of waiting ~30 seconds for 48-item serial page loads.

Screenshots (if applicable)

Include screenshots or recordings for UI changes.

PXL_20260807_184032099.mp4

Checklist

• Code builds successfully
• Code follows project style and conventions
• No unnecessary commented-out code
• No new warnings introduced