Add a drag-and-resize animation

A drawn pointer grabs the frame near its top edge, drags it across the
screen, lets go, then takes hold of one corner and pulls the frame to a
new size. Moves ease in and overshoot slightly before settling, and the
paths bow, so the motion reads as a hand rather than a tween.

The resize pins the opposite corner and keeps the aspect ratio locked —
a stretched video would read as broken, not as someone resizing — and
clamps the width to the room left before the corner leaves the screen.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tg15tLAuT6NrCE1ZxKVgDB

README.md

@@ -33,18 +33,24 @@ autoplay, so the first click is what unlocks audio. One click per session.
   whenever a length is still unknown.
 - The queue is saved to `queue.json` on every change and restored at startup.
 - Settings live in `config.js`: overlap length, frame size, drift speed, corner
-  screenshot interval and margin, port, and the selectable backgrounds and
-  animations. Anything the browser needs must also be mirrored in the
-  `/config.js` route in `server/index.js`.
+  screenshot interval and margin, the drag animation's size range, port, and
+  the selectable backgrounds and animations. Anything the browser needs must
+  also be mirrored in the `/config.js` route in `server/index.js`.
 
 ## Animations
 
-The video frame's movement changes with every track. Two animations ship today:
+The video frame's movement changes with every track. Three animations ship
+today:
 
 - **bounce** — diagonal drift, reflecting off the screen edges.
 - **corners** — the frame parks in a random corner and every 5 seconds a
   screenshot of it appears in the next of the three other corners, going
   clockwise. The frame never moves, so a screenshot can never cover it.
+- **drag** — a drawn mouse pointer travels to the frame, grabs it near its top
+  edge and drags it across the screen, lets go for a beat, then takes hold of
+  one corner and pulls the frame to a new size. The aspect ratio stays locked
+  and the frame stays on screen, so the resize reads as a window resize rather
+  than a stretch.
 
 The queue page's **Animation** buttons pin the player to one of them, which is
 how you look at a single animation without waiting for the cycle to reach it.