feat(ui): Mac-inspired layout with sidebar, details panel, and About page

Replace the modal About dialog with an embedded About page and introduce
a three-pane desktop layout: persistent sidebar navigation, flat station
list, right-side details panel, and compact player bar.

Load the GPLv3 license text from C++ and expose it to QML as context
data. Normalize i18n source strings to English, complete German and
Russian translations (133 strings each), and centralize page navigation
helpers in Main.qml. Simplify compact HeaderNavigation and extend
.gitignore for local build artifacts.

CONTRIBUTING.md

@@ -37,6 +37,14 @@ If you changed QML:
 qmllint src/qml/Main.qml src/qml/components/*.qml src/qml/theme/BearTheme.qml
 ```
 
+For UI layout work that should be tested separately from the default build tree:
+
+```bash
+cmake -S . -B build-maclayout -DCMAKE_BUILD_TYPE=Release
+cmake --build build-maclayout -j"$(nproc)"
+./build-maclayout/src/bearwave
+```
+
 Run unit tests after backend changes:
 
 ```bash
@@ -51,6 +59,7 @@ ctest --test-dir build --output-on-failure
 - Keep network operations asynchronous.
 - Preserve MPRIS behavior and user state compatibility.
 - When changing resources, register them in `src/qml.qrc`.
+- When changing the About page, keep the full GPL text resource visible and keep third-party technology notes accurate.
 
 ## Manual Checks
 
@@ -63,6 +72,7 @@ Please smoke-test the area you changed when possible:
 - favorites persist across restart
 - resume restores last station and volume
 - tray and MPRIS behavior still work
+- About page opens from sidebar/compact navigation, social links work, and the GPL license text is scrollable
 
 ## Pull Requests