fix(charts): zoom drag after Escape, after a lost release, and its label at the plot's edge - #2575

🟢 Confidence 10/10 · safe to merge. Each of the three gesture fixes is pinned by a DOM test that fails without it; only the label's px placement rests on the labelLeft unit test, since happy-dom has no layout.
_{no findings · tests covered · risk medium}

Fixes three drag-gesture defects in the linked zoom: Escape now keeps the drag so its trailing click is swallowed, a lost pointerup ends the drag, and the label is clamped inside the plot. Safe to merge.

• cancel() marks the drag cancelled and keeps it until its release
• onDragMove drops a drag whose event.buttons has no primary button
• The label leaves the band and labelLeft holds it inside the plot
• Eight DOM tests for the gesture in linked-cursor.dom.test.ts

_{bece67a · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}