fix(mobile): Library scroll + stale shelves; reader long-press word gate

[mrviduus]

Two mobile fixes (PM → architect → engineer → adversarial QA → fix cycle).

Library tab

• Scroll — the whole body now scrolls (the shelves carousels moved into the FlatList ListHeaderComponent; empty states use a ScrollView; safe-area bottom padding so the last row clears the tab bar + floating "+").
• Stale shelves — deleted/changed books lingered in "Continue reading"/"Recently added" because a 60s module-level cache wasn't invalidated. Now clearLibraryShelvesCache() bumps a version + notifies subscribers (useSyncExternalStore-style), so the live carousel refetches immediately — not only on refocus. Covers remove-from-library, delete-upload, mark-complete/uncomplete, cancel-upload, and pull-to-refresh.

Reader — long-press word gate

The word action (translation/Explain sheet + auto-TTS) used to fire on a light ≤350ms tap, causing accidental translations and wasted LLM tokens. Now:

• Fires only on a deliberate ~450ms long-press with <8px drift (haptic on engage).
• Quick tap on a word is swallowed (0 sheets, 0 LLM calls); quick tap on empty space still toggles the reading bars.
• touchcancel clears the timer (no ghost WordCard after an interrupted gesture); a drag past 16px after engage releases the selection-suppression window so native multi-word selection still works.
• Coachmark copy → "Press and hold a word". Mobile-only (injected readerHtml.ts); no web/reader-overlay change.

Verification

• apps/mobile tsc --noEmit clean; packages/shared vitest 149 green.
• Adversarial QA pass applied (touchcancel blocker, live-refresh, missed mutation sites, multi-select interference, dead-band all fixed).
• On-device validation owed (WebView not e2e-drivable): interrupted-gesture (no ghost card), native multi-word selection extend, in-tab delete → carousel updates without leaving the tab, haptic on engage, 450ms feel in scroll mode.

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