chore: Halkyon Learn moves into apps/learn

Its server, client, app and curator, and the tools that write its
assets (maps, Anki fixtures, icons), as they are; paths are fixed in
the commits that follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_flutter/macos/Runner/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -0,0 +1,68 @@
+{
+    "info": {
+        "version": 1,
+        "author": "xcode"
+    },
+    "images": [
+        {
+            "size": "16x16",
+            "idiom": "mac",
+            "filename": "app_icon_16.png",
+            "scale": "1x"
+        },
+        {
+            "size": "16x16",
+            "idiom": "mac",
+            "filename": "app_icon_32.png",
+            "scale": "2x"
+        },
+        {
+            "size": "32x32",
+            "idiom": "mac",
+            "filename": "app_icon_32.png",
+            "scale": "1x"
+        },
+        {
+            "size": "32x32",
+            "idiom": "mac",
+            "filename": "app_icon_64.png",
+            "scale": "2x"
+        },
+        {
+            "size": "128x128",
+            "idiom": "mac",
+            "filename": "app_icon_128.png",
+            "scale": "1x"
+        },
+        {
+            "size": "128x128",
+            "idiom": "mac",
+            "filename": "app_icon_256.png",
+            "scale": "2x"
+        },
+        {
+            "size": "256x256",
+            "idiom": "mac",
+            "filename": "app_icon_256.png",
+            "scale": "1x"
+        },
+        {
+            "size": "256x256",
+            "idiom": "mac",
+            "filename": "app_icon_512.png",
+            "scale": "2x"
+        },
+        {
+            "size": "512x512",
+            "idiom": "mac",
+            "filename": "app_icon_512.png",
+            "scale": "1x"
+        },
+        {
+            "size": "512x512",
+            "idiom": "mac",
+            "filename": "app_icon_1024.png",
+            "scale": "2x"
+        }
+    ]
+}