feat(photo-editor): Ajax Image Editor client (Photoshop-parity tools)

Photoshop-parity editor client: layers, selection/masking, brushes,
smart filters, LUT import, Quick Edit, mobile gestures, workspaces,
batch operations, and the service-worker versioning (v978->v1006).

Source: vendor/photocraft (ad1cff44) photo-editor client files, merged
onto upstream/dev (a8c147b2). Conflict resolution documented in
pr_work/A_conflicts.md; editor files taken from vendor/photocraft
(upstream's editor is an earlier snapshot of the same feature).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_editor_blend_modes_js.py

@@ -0,0 +1,60 @@
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+BLEND = ROOT / "static/js/editor/blend-modes.js"
+LAYER_CLIPPING = ROOT / "static/js/editor/layer-clipping.js"
+ADJUSTMENT_LAYER = ROOT / "static/js/editor/adjustment-layer.js"
+LAYER_GROUPS = ROOT / "static/js/editor/layer-groups.js"
+CONTROLS = ROOT / "static/js/editor/build/controls.js"
+CODEC = ROOT / "static/js/editor/document-codec.js"
+SW = ROOT / "static/sw.js"
+
+EXTRA_MODES = [
+    "dissolve",
+    "linear-burn",
+    "linear-dodge",
+    "darker-color",
+    "lighter-color",
+    "vivid-light",
+    "linear-light",
+    "pin-light",
+    "hard-mix",
+    "subtract",
+    "divide",
+]
+
+
+def test_blend_modes_module_shape():
+    src = BLEND.read_text(encoding="utf-8")
+    assert "export const NATIVE_BLEND_MODES" in src
+    assert "export const EXTRA_BLEND_MODES" in src
+    assert "export function blendDraw" in src
+    assert "export function isNativeBlendMode" in src
+    # Canvas natively supports linear-dodge via 'lighter'.
+    assert "linear-dodge" in src and "lighter" in src
+
+
+def test_extra_blend_modes_are_declared():
+    src = BLEND.read_text(encoding="utf-8")
+    for mode in EXTRA_MODES:
+        assert f"'{mode}'" in src or f'"{mode}"' in src, mode
+
+
+def test_blend_draw_is_wired_into_all_draw_paths():
+    for path in (LAYER_CLIPPING, ADJUSTMENT_LAYER, LAYER_GROUPS):
+        src = path.read_text(encoding="utf-8")
+        assert "blendDraw" in src, path
+        assert "blendDraw(" in src, path
+
+
+def test_blend_select_and_codec_offer_extra_modes():
+    controls = CONTROLS.read_text(encoding="utf-8")
+    codec = CODEC.read_text(encoding="utf-8")
+    for mode in EXTRA_MODES:
+        assert f'value="{mode}"' in controls, mode
+        assert f"'{mode}'" in codec or f'"{mode}"' in codec, mode
+
+
+def test_blend_modes_precached():
+    assert "/static/js/editor/blend-modes.js" in SW.read_text(encoding="utf-8")