add help docs and ?

docs/nodes/Draw Mask.md

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+# Draw Mask
+
+Paint a binary mask directly over an image preview. Pen size controls newly drawn strokes, the Clear Mask button removes all strokes, and invert flips the final binary output.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Background field whose dimensions define the mask size |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| mask | IMAGE | Binary mask image (painted regions = white, background = black, or inverted) |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| pen_size | INT | 12 | Brush diameter in pixels for newly drawn strokes (1–128) |
+| invert | BOOLEAN | False | When enabled, swaps painted and unpainted regions |
+| clear_mask | BUTTON | — | Clears all painted strokes |
+
+## Limitations
+
+- Strokes are stored as path data; very long painting sessions with many strokes may accumulate large state.
+- The mask resolution matches the input field resolution and cannot be changed independently.