add help docs and ?

docs/nodes/Mask Operations.md

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+# Mask Operations
+
+Apply boolean logic to two binary masks. Supports AND, OR, XOR, NAND, NOR, XNOR, directional subtraction (A minus B, B minus A), implication, pass-through, and constant true/false outputs.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| mask_a | IMAGE | Yes | First binary mask operand |
+| mask_b | IMAGE | Yes | Second binary mask operand |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| mask | IMAGE | Result of the boolean operation |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| operation | dropdown | and | Boolean operation: and, or, xor, xnor, nand, nor, a_minus_b, b_minus_a, a, b, not_a, not_b, a_implies_b, b_implies_a, false, true |
+
+## Limitations
+
+- Both masks must have the same pixel dimensions.