v1.7.10 — Click-to-update + rounded polish

Changed

• Polish pass v2 (updated design handoff): softer "new OS" corner radii
  across every surface (sidebar, cards, menus, modals, inputs — pills and
  circles untouched), including the inline-styled inputs in Sources/Settings
  add-forms and Onboarding; Monthly hero divider softened to match the calmer
  hairline system; signal badge/tooltip radii bumped to match. Song-row corner
  rounding adjusted to the new 18px container frame.
• Updates are now user-initiated, not automatic. The app no longer
  downloads updates or shows a restart dialog on its own — it only checks
  availability. Clicking the sidebar "Update to vX" pill is what installs:
  it downloads in place (pill shows "Updating…") and the app restarts itself.
  New POST /api/update/install route bridges the pill to the updater via
  global.__appUpdater; outside the packaged app (or on failure) the pill
  falls back to opening the releases page. A finished download still installs
  on quit (autoInstallOnAppQuit) if the user quits instead of restarting.