[sang765]

Summary

Fixes webtoon mode where the page counter and reading progress get stuck at 18/19 · 97% even after scrolling to the last page of the newest chapter.

Root causes

1. Current page never becomes the last page — ReaderViewModel.onCurrentPageChanged resolves the current page as the center of the visible range (first + last) / 2. When the last page is short (credits pages are common), the previous page's window is still partially visible at the bottom, so the center is always the second-to-last page. Additionally, the scroll dispatcher only emits events when item positions change — at max scroll positions freeze, so no further events can ever mark the last page. (Chapters whose last page fills the viewport worked, which is why the bug looked inconsistent.)
2. Stale state on exit — getCurrentState() probed the page under the last tap/long-press coordinates (sticky downY), so exiting the reader saved an older page: progress regressed in details screen and reopening started at 18/19 again.
3. Float overshoot — computePercent could produce values slightly above 1f when the chapter count doesn't divide evenly, failing isCompleted/isValid checks and breaking the 100% display.

Changes

• WebtoonReaderFragment: resolve the current page from viewport geometry — last page at the bottom edge, first page at the top edge, center of visible range otherwise; probe state from the layout manager instead of stale touch coordinates; re-report the page on SCROLL_STATE_IDLE (catches flings landing exactly at max scroll).
• WebtoonRecyclerView: scroll dispatcher also fires when at-top/at-bottom state flips (fires immediately when the edge is reached mid-drag).
• ReaderViewModel: clamp computePercent to 1f.
• TapGridDispatcher / ReaderActivity: visibility reverted to private for fields that no longer have external readers.

Testing

• Scroll to the end of the latest chapter → counter shows 19/19, percent 100%
• Exit reader → details screen shows 100%, reopening resumes at the last page
• Tap/long-press an image (action menu), scroll to the end, exit → state still saved at the last page
• Scrolling between chapters behaves as before; pull-to-next-chapter still triggers

[dragonx943]

Migrated to #168