fix(ui): restore triple-click paragraph selection

[backnotprop]

Summary

• Skip outside-click dismiss on multi-click (event.detail >= 2) in useDismissOnOutsideAndEscape
• One-line guard + comment in packages/ui/hooks/useDismissOnOutsideAndEscape.ts

Root Cause

Regression from 39b63c9 ("dismiss annotation toolbars on outside click and Escape", #182). That commit added a pointerdown capture listener to dismiss the annotation toolbar on outside click. During a triple-click:

1. 2nd mouseup — web-highlighter wraps the word in <mark>, toolbar mounts, dismiss hook starts listening
2. 3rd pointerdown (fires before mousedown) — dismiss hook fires → handleToolbarClose() removes the <mark> and normalises text nodes
3. 3rd mousedown — the DOM mutation in step 2 changed the element under the cursor (from <mark> to plain text), resetting the browser's click-count. The 3rd click is treated as detail=1 instead of detail=3
4. 3rd mouseup — window.getSelection().isCollapsed is true → no highlight → no toolbar

Fix

Guard handlePointerDown with event.detail >= 2. Multi-click pointerdowns are part of an active selection gesture — the web-highlighter CREATE handler already cleans up stale pending highlights when a new selection commits, so the eager dismiss is unnecessary.

Test plan

• Double-click a word → toolbar appears for the word
• Triple-click a paragraph → toolbar appears for the full paragraph/line
• Single-click outside toolbar → toolbar dismisses
• Double-click at a new location while toolbar is showing → old toolbar replaced by new word toolbar
• Press Escape → toolbar dismisses
• Code review: click outside annotation toolbar → still dismisses
• Mobile/touch: tap outside toolbar → still dismisses (touch detail is 0)

Fixes #544