Animate Hide Later Items with a paced staggered reveal

[MaplumeX]

What

Gives the Hide Later Items toggle a deliberate reveal rhythm instead of an instant layout swap: hidden rows collapse (fading out before the height closes, so text never looks squashed), revealed rows first open their space and then fade in, and newly revealed rows flash a brief tint so it's clear which items just came back.

Changes

• lib/laterReveal.ts (new) — single source of truth for the reveal pacing: revealExitOpacity() (opacity reaches 0 at 60% of the progress), revealEnterOpacity() (opacity starts rising at 30%), and flashRevealedRows(), which plays a short --primary-tinted background flash on the affected [data-selection-row] elements and fades back to each row's current background.
• lib/dnd.ts — useFlipList exposes a new captureReveal() that snapshots the DOM before the toggle re-renders and marks the snapshot as reveal. Exit/enter animations then use the slightly different opacity keyframes and, critically, bypass the MAX_ENTER_EXIT cap — a single toggle can legitimately move many rows at once.
• components/ui/collapse.tsx — new reveal prop applies the paced opacity keyframes to the height animation; new onOpen(element) callback fires when the expand animation starts (content already mounted), which lets callers kick off the row flash at the right moment.
• components/project/ProjectTaskLayout.tsx — calls captureReveal() on the render where the Later-items state flips, keyed off a hidingLater ref. taskMap now also includes the hidden source tasks so rows still exist in the DOM and can play their FLIP exit rather than disappearing a frame early. hasContent is recomputed from the visible tasks plus draft/headings, so a project whose Later items are all hidden renders the empty state correctly.
• pages/AreaDetail.tsx — wraps LaterItemSections in <Collapse reveal onOpen={flashRevealedRows}>, keyed by area id so switching areas doesn't animate. Spacing moves into pt/-mt so the gap collapses with the height instead of jumping on unmount.
• components/common/LaterItemsToggle.tsx — the label fades in on toggle via a keyed span.

Tests

• dnd.test.tsx: reveal-mode ghost fade-out keyframes, delayed enter fade-in with row highlight, no highlight on untouched rows, and no MAX_ENTER_EXIT cap when revealing.
• collapse.test.tsx: reveal keyframes for both directions and the onOpen callback contract.
• ProjectTaskLayout.test.tsx: end-to-end hide/show of a Later task, asserting the ghost exit and the paced re-entry of the revealed row.