fix(terminal): require touch slop before starting finger scroll

[ulite-Amr]

Problem

Modifier.scroll started scrolling on the first drag event with no touch-slop gate. Effects:

• Accidental micro-movements / finger jitter scrolled the terminal.
• dragEvent.consume() ran on every move event (even sub-pixel drift from a still finger). Compose's tap detector cancels long-press when movement is consumed by another gesture, so long-press to select text was unreliable — any drift during the hold canceled it.

Additionally, previousPosition was never updated while selectionState.isActive; if selection deactivated mid-gesture, the first scroll frame used a stale position and jumped a large delta.

Fix

• Gate finger scrolling behind passedTouchSlop (viewConfiguration.touchSlop), matching the standard drag-gesture arbitration used by detectDragGestures.
• Only consume movement past the slop — a still finger no longer has its long-press interrupted, so long-press text selection now fires reliably.
• Keep previousPosition in sync during selectionState.isActive, so a selection drag that becomes a scroll starts with a fresh delta (no jump).

Verification

Finger scrolling, long-press selection, and selection-handle drags tested on-device via a signed release build from the fork's CI.