The gesture is classified once, on the first movement past 8 px
(`_panLock`), but `_stagePointerUp` ignored that decision and asked
`swipeTarget()` again from the raw start→end vector — audit DEV-1DA1-02.
So a CURVED gesture could be both: a small vertical lead-in locked
`pan`, the plan started following the finger, the trajectory then swept
far sideways, and lifting the finger landed the user on another storey.
On a wall tablet that is the worst kind of surprise — you watch the plan
drag along and end up on a different floor.
The lock is now final: with `_panLock === 'pan'` the floor never
changes, whatever the overall vector looks like, and only a gesture
locked as `swipe` may reach `swipeTarget()`. A motionless tap locks
nothing, so the double-tap zoom reset is untouched.
Regression: demo/smoke_kiosk_pan_lock.mjs — the auditor's curved pan
(both directions and a long diagonal), the mirror case of a swipe that
bends vertically (it never pans, and if it stops qualifying it simply
does nothing), plus the straight swipe / straight pan / double tap /
zoomed-in cases. docs/CANVAS.md §5 and docs/TESTING.md updated.
