Onboarding, clock alignment, and calendar flyout fixes.

Added
- Launch-at-login onboarding step.
- Live Analog Companion setup: menu-bar preview plus real-time
  detection of whether the macOS clock is already analog.
- "Open Clock Settings" deep-link in the right-click analog tip,
  suppressed when the macOS clock is already analog.
- SystemClockState helper for reading the live macOS clock style.

Changed
- Wall-clock-aligned ticking for the menu-bar clock and flyout
  header; the blinking separator toggles on the half-second.
- Reordered onboarding mode cards (Calendar Icon first).
- Rewrote/trimmed README; screenshot now bundled at docs/app.png.

Fixed
- Weekday header dropped the duplicate "T"/"S" columns; all seven
  day letters now render.
- Flyout's behind-window material no longer leaks square corners.

Bump version to 0.2.0 (build 2) and add CHANGELOG.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>