Add fork features: host view sync, grouping, image compress, freistellen

Host can force all clients to their camera; selection Group/Ungroup with
synced groupIds; WebP/PNG preprocess and Tower rembg/white-key freistellen
on insert or via selection actions (save format 0.7 / INFPNT000007).

Co-authored-by: Cursor <cursoragent@cursor.com>

FORK.md

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+# Fork features (copilot/infinipaint)
+
+Upstream: [ErrorAtLine0/infinipaint](https://github.com/ErrorAtLine0/infinipaint)  
+Forgejo: https://forgejo.fsociety00.cc/copilot/infinipaint
+
+Save format: `INFPNT000007` / version `0.7.0-fork` (not network-compatible with stock 0.6.x peers).
+
+## Bring Everyone Here (host)
+
+In the player list, the lobby host gets **Bring Everyone Here**. Clients receive `CLIENT_FORCE_CAMERA_JUMP` and run the same `smooth_move_to` path as **Jump To**.
+
+## Group / Ungroup
+
+With a multi-selection (images, text boxes, shapes, …), use **Group** / **Ungroup** in the selection panel. Grouped objects auto-expand into the selection so they transform together. Membership syncs via `SET_COMPONENT_GROUP_IDS`.
+
+## Image compression
+
+Settings → **Images**:
+
+- Compress on insert (default on)
+- Format: Keep / WebP / PNG
+- WebP quality
+
+Selection toolbar: **Compress Images** re-encodes already placed images.
+
+## Freistellen
+
+Settings → **Images**:
+
+- Freistellen on insert
+- Modes: White background (always), or rembg **Schnell** (`silueta`) / **Allgemein** (`bria-rmbg`) when Tower rembg is installed (`~/.local/share/tower-rembg` or `rembg` on `PATH`)
+
+Selection: **Freistellen** applies the configured mode to selected images (then compresses).