fix: crop rotated images, radius in px, modals block timeline

Replays the 13 open bug reports on alyssaxuu/motionity against this fork.
Nine were already fixed by the earlier audit and one (#8, video from the
search tab) needs a Pixabay API key to reproduce; these are the three that
were still broken.

#23 - border radius behaved like a percentage. fabric applies rx/ry before
the object's scale and shapes are resized by scaling, so a radius typed as
20 drew at 60px on a rect scaled 3x while the panel still read 20. A new
cornerRadius property keeps the pixel value the user asked for, rx/ry are
derived from it and re-derived whenever the scale changes, and old projects
fall back to rx * scaleX.

#27 - cropping a rotated image cropped the wrong region. crop() compared
canvas-space edges and covered only three of the four quadrants, so it did
nothing at all when the crop window was centred on the image. It now works
in the image's own frame, clamps the region to the bitmap and re-centres the
object on what it kept; the crop window carries the image's angle and the
expand-to-full-bitmap shift in cropImage is rotated the same way.

#1 - modals are painted over the timeline but never took its pointer events,
so the resize handle, seekbar, keyframes and layer bars all reacted to a drag
behind the dialog. All four now bail while a modal is open.

Verified in Chromium: 20px draws a 20px corner at scale 1 and scale 3 and
survives save, JSON round-trip and reload; at 0, 30 and 45 degrees the pixels
under the crop window are unchanged by the crop and everything outside it is
dropped; a real drag on the timeline handle with the export modal open leaves
the timeline height untouched. WEBM export and a non-rotated crop still work.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

TODO-FIXES.md

@@ -315,3 +315,56 @@ held the Playwright profile lock), so the following still needs a manual pass:
    console shows `Rendering n%` (frame-accurate path) and not
    `Falling back to the real-time encoder`
 4. Play the result: check audio is in sync and the video layer is not smeared
+
+---
+
+## Upstream open issues (alyssaxuu/motionity)
+
+The 13 bug reports still open upstream were replayed in Chromium against this
+fork. Nine were already fixed by the audit above — mp4 export (#16), blank
+render (#25), image download (#10), audio on download (#30), filters not
+retained (#24), `EyeDropper is not defined` (#15, #18), the endless
+*Loading video…* (#28) and text selection while resizing the timeline (#5).
+GIF export (#21) works through the same ffmpeg path. #8 (video from the search
+tab) needs a Pixabay API key, so it stays untested; #29 and #4 carry no
+reproducer. The remaining three are fixed here:
+
+- [x] **#23 — Border radius behaved like a percentage** — `src/js/functions.js`,
+  `src/js/ui.js`, `src/js/events.js`, `src/js/database.js`
+  fabric applies `rx`/`ry` before the object's scale, and shapes are resized by
+  scaling, so a radius typed as 20 drew at 60 px on a rect scaled 3x while the
+  panel — which read `rx` back raw — still said 20. A new `cornerRadius` property
+  stores the pixel value the user asked for; `rx`/`ry` are derived from it
+  (`setCornerRadius`) and re-derived on `object:scaling` / `object:modified`
+  (`syncCornerRadius`), so the same number means the same pixels at any size.
+  `cornerRadius` was added to the four serialised property lists, and
+  `getCornerRadius` falls back to `rx * scaleX` for projects saved before it
+  existed. Known limit, unchanged from before: if `scaleX` is *keyframed*, the
+  drawn radius still varies over the animation.
+  Verified: typed 20 px draws a 20 px corner at scale 1 and at scale 3, the
+  panel keeps reading 20, and the value survives save, JSON round-trip and a
+  page reload.
+
+- [x] **#27 — Cropping a rotated image** — `src/js/functions.js`
+  `crop()` compared canvas-space edges and covered only three of the four
+  quadrants, so any rotated image cropped the wrong region — and nothing at all
+  when the crop window was centred on it, since all three branches need a
+  strictly positive offset. The guards added in the audit stopped the crash but
+  left the geometry wrong. `crop()` now works in the image's own frame
+  (`rotateVector`), clamps the region to the bitmap, and re-centres the object on
+  the region it kept; the crop window is created with the image's `angle`, and
+  the "expand back to the full bitmap" shift in `cropImage` is rotated the same
+  way. The four-branch soup is gone.
+  Verified: at 0°, 30° and 45°, the pixels under the crop window are byte
+  identical before and after the crop, everything outside it is dropped, and
+  crop mode exits cleanly.
+
+- [x] **#1 — A modal did not block the timeline** — `src/js/functions.js`
+  Modals are painted over the timeline but never took its pointer events, so the
+  resize handle, the seekbar, keyframes and layer bars all still reacted to a
+  drag behind the dialog. The onboarding modal from the report does not exist in
+  the open-source build; the export, import/export and credits modals all had
+  the bug. `dragTimeline`, `dragSeekBar`, `dragKeyframe` and `dragObjectProps`
+  now bail while `.modal-open` is present.
+  Verified: with the export modal open a real mouse drag on the handle leaves
+  the timeline height untouched, and dragging works again once it closes.