Add bg park postitions. Closes #18

web/assets/backgrounds/image_spec.md

@@ -46,6 +46,7 @@ This file tells the web UI where your letters/targets are located in **physical
 ```json
 {
   "hasAlphabet": true,
+  "parkPosition": { "x": 0, "y": 80 },
   "bounds": {
     "xMin": -150,
     "xMax": 150,
@@ -60,9 +61,20 @@ This file tells the web UI where your letters/targets are located in **physical
 }
 ```
 - **hasAlphabet**: (Optional, boolean) If `true`, this background is used for the "Input Text" feature. The letters in `spots` are used to spell out typed input.
+- **parkPosition**: (Optional, object) Defines a background-specific "Park Position" or resting spot where the arm can go when not actively in use. If omitted, defaults to `{ "x": 0, "y": 0 }`.
 - **bounds**: Defines the physical bounding box (in mm) that your background image represents. This automatically adjusts the UI's aspect ratio and coordinate mapping!
 - **spots**: Array of target objects.
-- **id**: Unique identifier for the dropdown list.
-- **label**: Human-readable text shown on the UI.
-- **x**: The X coordinate in physical mm (`-150` to `+150`).
-- **y**: The Y coordinate in physical mm (`-30` to `+145`).
+  - **id**: Unique identifier for the dropdown list.
+  - **label**: Human-readable text shown on the UI.
+  - **x**: The X coordinate in physical mm (`-150` to `+150`).
+  - **y**: The Y coordinate in physical mm (`-30` to `+145`).
+
+## 5. Excluded Zones (No-Go Zones)
+
+When defining spots or the `parkPosition`, you **must avoid** the central mechanism housing. The SCARA arm will reject commands that enter this region to prevent mechanical collisions.
+
+The exact exclusion box (the "No-Go Zone") is:
+- **X Range:** `-30` mm to `+30` mm
+- **Y Range:** `-10` mm to `+40` mm
+
+Make sure that your `parkPosition` and all clickable spots lie outside this rectangle.