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/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(