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/scripts/build-core.sh

@@ -44,6 +44,13 @@ export MACOSX_DEPLOYMENT_TARGET="${MACOSX_DEPLOYMENT_TARGET:-15.0}"
 # This never touches the Rust crate — it only changes how the build is invoked.
 export CARGO_PROFILE_DEV_STRIP=none
 
+# The workspace `[profile.release] lto = "thin"` corrupts host proc-macro / build
+# script dylibs when cross-compiling ("mis-aligned LINKEDIT string pool"). Cargo
+# forbids overriding `lto` per build-override, so disable thin LTO for the whole
+# release build here — the crate is still fully optimized (opt-level 3, debuginfo
+# stripped), which is what shrinks the static lib. This never edits the Cargo crate.
+export CARGO_PROFILE_RELEASE_LTO=false
+
 IOS_TARGET="aarch64-apple-ios"
 SIM_ARM_TARGET="aarch64-apple-ios-sim"
 SIM_X64_TARGET="x86_64-apple-ios"