feat(ui): clarify selection mode, remove reader filmstrip

[everpcpc]

What

Two reader/browse UI cleanups from the simulator review round:

• Remove the reader page filmstrip. The paged-reader controls overlay no longer shows the thumbnail filmstrip row; the bottom overlay is just the page badge and the progress bar. Visual page browsing now lives entirely in the existing "Go to Page" sheet (large preview carousel + slider), reachable from the page badge.
• Clarify multi-select state. In selection mode, unselected grid cards and list rows now shrink slightly toward their own center and gray out (scale + opacity + saturation, animated); selected items return to full size and brightness. The selection checkmark moves to the bottom-trailing corner of the cover on grid cards (rendered through the card's existing cover badge slot) and to the trailing edge on list rows.

Why

• The filmstrip duplicated the page jump sheet with much smaller, unreadable thumbnails; its one unique affordance (drag-scrubbing pages) fought the finger instead of tracking it. The jump sheet does the same job with full-size previews.
• In selection mode it was hard to tell at a glance which items were picked: the only signal was a small circle at the top-leading corner. Receding unselected items makes the picked set read instantly, and the bottom-trailing checkmark matches the platform convention.

Validation

• make format, make build (iOS / macOS / tvOS) all pass.
• iOS simulator (iPhone 18 Pro): opened a 199-page book — overlay shows only page badge + progress bar; "Go to Page" sheet opens from the badge and jumps correctly. Series detail grid and list layouts: entering selection mode dims/shrinks all items in place without disturbing the grid; tapping toggles the checkmark at the cover's bottom-trailing corner (grid) / row trailing edge (list); selected items return to full emphasis.