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.

shared/build.gradle.kts

@@ -110,6 +110,55 @@ val generateDiagnosticsBuildConfig by tasks.registering {
 	}
 }
 
+// App-wide public constants (privacy policy URL, …) from the shared app.properties,
+// so Apple and KMP read one source of truth instead of hardcoding values.
+val appProperties = java.util.Properties().apply {
+	rootProject.file("app.properties").inputStream().use(::load)
+}
+val privacyPolicyUrl: String = appProperties.getProperty("PRIVACY_POLICY_URL")?.trim().orEmpty()
+check(privacyPolicyUrl.isNotEmpty()) { "PRIVACY_POLICY_URL must be set in app.properties" }
+
+val appConfigDir = layout.buildDirectory.dir("generated/appconfig/commonMain/kotlin")
+val generateAppConfig by tasks.registering {
+	group = "build"
+	description = "Generates AppConfig from the shared app.properties"
+	val outputDir = appConfigDir
+	val privacy = privacyPolicyUrl
+	inputs.property("PRIVACY_POLICY_URL", privacy)
+	outputs.dir(outputDir)
+	doLast {
+		val packageDir = outputDir.get().asFile.resolve("com/vnidrop/app")
+		packageDir.mkdirs()
+		fun esc(value: String): String = buildString {
+			for (ch in value) {
+				when (ch) {
+					'\\' -> append("\\\\")
+					'"' -> append("\\\"")
+					'\n' -> append("\\n")
+					'\r' -> append("\\r")
+					'\t' -> append("\\t")
+					'$' -> append("\\$")
+					else -> append(ch)
+				}
+			}
+		}
+		packageDir.resolve("AppConfig.kt").writeText(
+			"""
+			|package com.vnidrop.app
+			|
+			|/**
+			| * Generated by shared/build.gradle.kts from the shared app.properties.
+			| * Single source of truth for app-wide public constants (also used by Apple).
+			| */
+			|object AppConfig {
+			|	const val PRIVACY_POLICY_URL: String = "${esc(privacy)}"
+			|}
+			|
+			""".trimMargin(),
+		)
+	}
+}
+
 kotlin {
 	androidTarget {
 		compilerOptions {
@@ -122,6 +171,7 @@ kotlin {
 	sourceSets {
 		commonMain {
 			kotlin.srcDir(files(diagnosticsBuildConfigDir).builtBy(generateDiagnosticsBuildConfig))
+			kotlin.srcDir(files(appConfigDir).builtBy(generateAppConfig))
 		}
 		androidMain.dependencies {
 			implementation(libs.androidx.activity.compose)

shared/src/commonMain/kotlin/com/vnidrop/app/feature/settings/AboutSettings.kt

@@ -52,7 +52,7 @@ import vnidrop.shared.generated.resources.os_version_title
 import vnidrop.shared.generated.resources.value_unavailable
 import vnidrop.shared.generated.resources.version_title
 
-private const val PrivacyPolicyUrl = "https://github.com/vnidrop/vnidrop"
+private val PrivacyPolicyUrl = com.vnidrop.app.AppConfig.PRIVACY_POLICY_URL
 
 @Composable
 internal fun AboutSettings(

shared/src/jvmTest/kotlin/com/vnidrop/app/AppConfigTest.kt

@@ -0,0 +1,40 @@
+package com.vnidrop.app
+
+import java.io.File
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+/**
+ * Verifies the build-time [AppConfig] (generated from the shared `app.properties`)
+ * exposes the expected, well-formed values to the shared UI.
+ */
+class AppConfigTest {
+	@Test
+	fun privacyPolicyUrlIsTheExpectedHttpsEndpoint() {
+		assertTrue(AppConfig.PRIVACY_POLICY_URL.startsWith("https://"), "must be https")
+		assertEquals("https://vnidrop.sudosy.fr/privacy/", AppConfig.PRIVACY_POLICY_URL)
+	}
+
+	@Test
+	fun privacyPolicyUrlMatchesTheSharedConfigFile() {
+		// Cross-check the generated constant against the single source of truth so a
+		// broken codegen (or drift) is caught, not just a hardcoded copy.
+		assertEquals(privacyUrlFromAppProperties(), AppConfig.PRIVACY_POLICY_URL)
+	}
+
+	private fun privacyUrlFromAppProperties(): String {
+		var dir: File? = File(System.getProperty("user.dir")).absoluteFile
+		repeat(8) {
+			val candidate = File(dir, "app.properties")
+			if (candidate.isFile) {
+				return candidate.readLines()
+					.firstOrNull { it.startsWith("PRIVACY_POLICY_URL=") }
+					?.substringAfter("PRIVACY_POLICY_URL=")
+					?: error("PRIVACY_POLICY_URL missing in ${candidate.path}")
+			}
+			dir = dir?.parentFile
+		}
+		error("app.properties not found from ${System.getProperty("user.dir")}")
+	}
+}