feat(docs): add detailed documentation for ParseStringToBBox node including inputs, outputs, and usage tips

web/docs/ParseStringToBBox.md

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+**Summary**:  
+Parses a JSON-style bounding box string into integer coordinates and returns width and height. The node expects the exact nested-list format: `[[x1, y1, x2, y2]]`.
+
+**Inputs**
+- **bboxString**: `STRING` — A JSON string containing one inner list with four numeric values. Example: `[[170.64, 71.72, 300.56, 238.28]]`.
+
+**Outputs**
+- **x1**: `INT` — Rounded x1 coordinate
+- **y1**: `INT` — Rounded y1 coordinate
+- **x2**: `INT` — Rounded x2 coordinate
+- **y2**: `INT` — Rounded y2 coordinate
+- **width**: `INT` — Rounded width computed as `x2 - x1`
+- **height**: `INT` — Rounded height computed as `y2 - y1`
+
+**Usage Tips**
+- The node strictly parses JSON. Provide a properly formatted JSON string (including the outer and inner brackets) — other formats are not accepted.
+- If parsing fails or the structure is incorrect, the node raises a `ValueError` (this will show as an error when executing the node).
+- Coordinates are parsed as floats internally then rounded to the nearest integer before being returned.
+- Use the returned `width` and `height` if you need integer sizes (e.g., for cropping or annotations).
+
+**Example**
+Input string:
+
+```
+[[170.6425323486328, 71.72273254394531, 300.5597229003906, 238.28350830078125]]
+```
+
+Outputs:
+
+- `x1`: `171`
+- `y1`: `72`
+- `x2`: `301`
+- `y2`: `238`
+- `width`: `130`
+- `height`: `166`
+
+See developer documentation for implementation notes and examples: `../../dev-docs/nodes/parse-string-to-bbox/PARSE_STRING_TO_BBOX.md`