refactor: Extract zoom drag handlers to functions in zoom._hs

- Move inline drag handling (~35 lines) to external functions (~4 lines)
- Add isZoomDragTarget(el), startZoomDrag(), moveZoomDrag(), endZoomDrag()
- Note: 'target' is reserved in hyperscript, use 'el' for parameters
- Drag state stored on element (_isDragging, _initialX, _initialY)

Zoom control HTML now has clean, minimal hyperscript handlers.

static/hyperscript/zoom._hs

@@ -139,3 +139,64 @@ def toggleZoomControl()
     end
   end
 end
+
+-- ==============================================================================
+-- ZOOM CONTROL DRAG HANDLERS
+-- ==============================================================================
+-- Check if drag target is valid (not a button or input)
+def isZoomDragTarget(el)
+  if el.tagName is 'INPUT'
+    return false
+  end
+  if el.tagName is 'BUTTON'
+    return false
+  end
+  if el.matches('.zoom-slider, .zoom-close-btn, .zoom-reset-btn, .zoom-value')
+    return false
+  end
+  if el.closest('.zoom-close-btn')
+    return false
+  end
+  if el.closest('.zoom-reset-btn')
+    return false
+  end
+  return true
+end
+
+-- Start dragging zoom control
+def startZoomDrag(control, clientX, clientY)
+  set control._isDragging to true
+  set control's *transition to 'none'
+  set rect to control.getBoundingClientRect()
+  set control._initialX to clientX - rect.left
+  set control._initialY to clientY - rect.top
+end
+
+-- Handle drag move
+def moveZoomDrag(control, clientX, clientY)
+  if control._isDragging is not true
+    return false
+  end
+  set currentX to clientX - control._initialX
+  set currentY to clientY - control._initialY
+  set maxX to window.innerWidth - control.offsetWidth
+  set maxY to window.innerHeight - control.offsetHeight
+  set currentX to Math.max(0, Math.min(currentX, maxX))
+  set currentY to Math.max(0, Math.min(currentY, maxY))
+  set control's *left to `${currentX}px`
+  set control's *bottom to `${window.innerHeight - currentY - control.offsetHeight}px`
+  set control's *transform to 'none'
+  return true
+end
+
+-- End drag and save position
+def endZoomDrag(control)
+  if control._isDragging is not true
+    return false
+  end
+  set control._isDragging to false
+  set control's *transition to 'all 0.3s ease'
+  set position to { bottom: control.style.bottom, left: control.style.left }
+  set localStorage['cv-zoom-position'] to JSON.stringify(position)
+  return true
+end