chore(release): bump version to 0.42.0

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/release-notes.md.tmpl

@@ -3,6 +3,7 @@
 Notebook app for pen, touch and mouse on Linux (tested on Zorin OS 18 / Ubuntu 24.04).
 
 ### Highlights:
+- **Nextcloud built in**: ☰ → Storage location → Nextcloud syncs the notebooks directly with your Nextcloud – also on Android and without a sync client. Enter the server address (private servers in a subfolder, with their own port or a self-signed certificate work too), sign in in the browser; the app gets an app password of its own that "Disconnect" revokes again. Syncing runs every 30 seconds and shortly after saving and keeps working offline; a page changed on two devices is kept twice, deleted notebooks and pages go into the trash on both sides, changes arriving for the open notebook wait until it is saved (Issue #49)
 - **Android toolbar fix**: The toolbar and menus stay clear of the status bar, the navigation bar and the camera cutout, so the topmost button (📚 notebooks) can be tapped again; in landscape the page is centered between the side bars. Nothing changes on Linux and Windows (Issue #50)
 - **Computing formulas (experimental)**: Turn on in ☰ → Input ("Compute formulas after “=”"). After a handwritten `=` and a short pause, the result appears next to it together with what was read, e.g. `2⁴ = 16` or `(x + 3)² = x² + 6x + 9`; tapping it with the pen or clicking inserts it as text in the ink color and as high as the handwriting. Digits, `+ − · : /`, parentheses, exponents, fraction bars, decimal commas and `x`, `y`, `a`, `b` are read; numbers are computed exactly, expressions with variables multiplied out. Recognition runs offline without machine learning – feedback with real handwriting welcome (Issue #46)
 - **Android**: `ink-notes_<version>_arm64.apk` brings ink-notes to Android 8 and newer (64-bit ARM) – download it on the device and open it to install. The pen is told apart from fingers (pressure, pen buttons, eraser end, palm rejection), text fields open the soft keyboard, import and inserting images use the system file dialog, and exports are saved to `Download/ink-notes` (Android 10 and newer). Notebooks live in the app's own storage and are removed when uninstalling; updates are installed by opening the new APK. Nothing changes on Linux and Windows