refactor(md-deck): pos string and yaml copy output

Replace per-axis x1/y1/x2/y2 layer fields with a single
pos string (x1,y1-x2,y2) matching the compact layers format.

When a deck is configured via a yaml/tag codeblock (data-config),
the copy button now emits a yaml/tag block serialized from current
store state so template layers round-trip.

src/components/md-deck/config.test.ts

@@ -18,7 +18,7 @@ describe("layersToConfigs", () => {
 
   test("parses structured list with prop layers", () => {
     const layers = layersToConfigs([
-      { prop: "name", x1: 1, y1: 1, x2: 5, y2: 2, font: 12 },
+      { prop: "name", pos: "1,1-5,2", font: 12 },
     ]);
     expect(layers).toHaveLength(1);
     expect(layers[0]).toMatchObject({
@@ -35,7 +35,7 @@ describe("layersToConfigs", () => {
 
   test("parses structured list with template layers", () => {
     const layers = layersToConfigs([
-      { template: "**{{name}}**", x1: 1, y1: 3, x2: 5, y2: 8, align: "l" },
+      { template: "**{{name}}**", pos: "1,3-5,8", align: "l" },
     ]);
     expect(layers).toHaveLength(1);
     expect(layers[0]).toMatchObject({
@@ -50,6 +50,12 @@ describe("layersToConfigs", () => {
     });
   });
 
+  test("defaults placement when pos is missing or invalid", () => {
+    const layers = layersToConfigs([{ prop: "x" }, { prop: "y", pos: "bogus" }]);
+    expect(layers[0]).toMatchObject({ x1: 1, y1: 1, x2: 2, y2: 2 });
+    expect(layers[1]).toMatchObject({ x1: 1, y1: 1, x2: 2, y2: 2 });
+  });
+
   test("returns [] for absent/empty input", () => {
     expect(layersToConfigs()).toEqual([]);
     expect(layersToConfigs("")).toEqual([]);
@@ -81,8 +87,8 @@ describe("normalizeDeckConfig", () => {
   test("normalizes layers and back_layers", () => {
     const cfg = normalizeDeckConfig({
       layers: [
-        { prop: "name", x1: 1, y1: 1, x2: 5, y2: 1 },
-        { template: "{{body}}", x1: 1, y1: 2, x2: 5, y2: 8 },
+        { prop: "name", pos: "1,1-5,1" },
+        { template: "{{body}}", pos: "1,2-5,8" },
       ],
       back_layers: "logo:1,1-2,2",
     });