Add a fast scroller and fix row accessibility labels #75

What

A long flat list has no way to jump by letter. Rows also read the title twice to TalkBack, and the progress and download marks have no labels.

Bite

At 50k books there is no practical way to reach M or T by scrolling. TalkBack users get noisy rows.

Proposed shape

• Fast scroller with a letter bubble for title sort.
• Merge the row semantics so the title reads once, and add content descriptions for progress and download state.

Why not in the big-library build

It is new UI and an accessibility pass, separate from load cost.

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