feat(config): shared app.properties for app-wide constants

Add a single source of truth (root app.properties) for public app-wide
constants, injected at build time on both platforms instead of hardcoding.

- Apple: generate-appconfig.sh -> Generated/AppConfig.swift (wired into
  `make apple-app-config`), consumed as AppConfig.privacyPolicyURL.
- KMP: generateAppConfig task -> AppConfig.kt (mirrors DiagnosticsBuildConfig),
  consumed as AppConfig.PRIVACY_POLICY_URL.

Replaces the stale hardcoded privacy-policy URL on both sides with
https://vnidrop.sudosy.fr/privacy/.

Also fix the Apple release core build: disable release LTO in build-core.sh
(Cargo forbids lto in a build-override) to avoid the proc-macro
"mis-aligned LINKEDIT string pool" corruption, so release archives are
compact instead of shipping the debug core.

Update the app icon.

Tests: shell test for the generator (escaping, missing/duplicate key),
plus XCTest and jvmTest asserting the generated value matches app.properties.

apple/VniDrop/Features/Settings/SettingsSections.swift

@@ -375,7 +375,7 @@ struct StorageSettings: View {
 struct AboutSettings: View {
 	@ObservedObject var model: SettingsModel
 
-	private static let privacyPolicyURL = URL(string: "https://github.com/vnidrop/vnidrop")!
+	private static let privacyPolicyURL = AppConfig.privacyPolicyURL
 
 	var body: some View {
 		Section {

apple/VniDrop/Resources/AppIcon.icon/icon.json

@@ -1,62 +1,57 @@
 {
-	"fill": {
-		"linear-gradient": [
-			"extended-gray:1.00000,1.00000",
-			"display-p3:0.55433,0.59923,0.92884,1.00000"
-		]
-	},
-	"groups": [
-		{
-			"blend-mode": "normal",
-			"blur-material": null,
-			"layers": [
-				{
-					"image-name": "Mask.svg",
-					"name": "Mask"
-				}
-			],
-			"lighting": "individual",
-			"refractivity": {
-				"depth": 0.5,
-				"enabled": true,
-				"strength": 0
-			},
-			"shadow": {
-				"kind": "neutral",
-				"opacity": 0.6
-			},
-			"specular": true,
-			"translucency": {
-				"enabled": true,
-				"value": 0.8
-			}
-		},
-		{
-			"layers": [
-				{
-					"image-name": "Drop.svg",
-					"name": "Drop"
-				},
-				{
-					"image-name": "U.svg",
-					"name": "U"
-				}
-			],
-			"lighting": "combined",
-			"shadow": {
-				"kind": "neutral",
-				"opacity": 0.6
-			},
-			"translucency": {
-				"enabled": true,
-				"value": 0.4
-			}
-		}
-	],
-	"supported-platforms": {
-		"circles": [
-			"watchOS"
-		],
-		"squares": "shared"
-	}
-}
+  "fill" : {
+    "linear-gradient" : [
+      "extended-gray:1.00000,1.00000",
+      "srgb:0.84942,0.81480,0.95401,1.00000"
+    ]
+  },
+  "groups" : [
+    {
+      "blend-mode" : "normal",
+      "blur-material" : null,
+      "layers" : [
+        {
+          "image-name" : "Mask.svg",
+          "name" : "Mask"
+        }
+      ],
+      "lighting" : "individual",
+      "shadow" : {
+        "kind" : "neutral",
+        "opacity" : 0.6
+      },
+      "specular" : true,
+      "translucency" : {
+        "enabled" : true,
+        "value" : 0.8
+      }
+    },
+    {
+      "layers" : [
+        {
+          "image-name" : "Drop.svg",
+          "name" : "Drop"
+        },
+        {
+          "image-name" : "U.svg",
+          "name" : "U"
+        }
+      ],
+      "lighting" : "combined",
+      "shadow" : {
+        "kind" : "layer-color",
+        "opacity" : 0.8
+      },
+      "translucency" : {
+        "enabled" : true,
+        "value" : 0.4
+      }
+    }
+  ],
+  "supported-platforms" : {
+    "circles" : [
+      "watchOS"
+    ],
+    "squares" : "shared"
+  }
+}