photoshop_recipe_frequency_separation

Build a frequency separation stack (Low + High) on top of the active layer for hands-on retouching. Does not apply any smoothing itself — the user paints into the layers afterwards. Users often say: frequency separation, split texture and color, manual retouch setup. Use when: the user explicitly wants frequency separation setup, typically for portrait or product retouching. Do NOT use when: the user wants a one-shot result without painting — use photoshop_recipe_enhance_portrait instead. Returns: { ok, summary, details: { radius_px, group_name } }. Preconditions: active document with a NORMAL raster active layer. Side effects: appends a "Frequency Separation" layer group with 2 prepared layers; one undo reverts everything.