feat(menu): #79 slice 3 — Look & Feel › Auto theme (completes #79)

Adds an "Auto theme (on/off)" row to Look & Feel and an `autotheme`
submenu: toggle the feature, pick the day/night themes (from
`nomarchy-theme-sync list`), and set the sunrise/sunset times (HH:MM,
validated). This is the menu surface over settings.autoTheme, completing
the auto time-of-day theme feature (slices: CLI / timer / menu).

Enabling writes the flag and defaults the summer-day/summer-night pair
--no-switch, then runs `auto --force`, so a single rebuild both installs
the timer and applies the correct theme for now. Disabling is instant
(--no-switch): the flag flips and `auto` self-gates, so the lingering
timer no-ops until the next rebuild. Day/night/time writes are live
--no-switch (read by `auto` at tick time).

Verification: V1 — HM generation builds (bash -n on nomarchy-menu at
build) + bash -n on the built menu. Logic test with stubbed
rofi/theme-sync/notify: selecting the toggle from off runs exactly `set
day/night/enable ... --no-switch` then `auto --force` — the intended
one-rebuild path. V0 flake check green. All three #79 slices shipped;
the live timer switch across sunset is a real-session (V3) check on a
Nomarchy machine.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/VISION.md

@@ -92,7 +92,7 @@ Reference: [HARDWARE.md](HARDWARE.md) §4–§5, §10.
 | Idea | Intent | Notes |
 |------|--------|-------|
 | **Fewer themes, sharper** | Finish or quarantine neon-glass; invest in whole-swap quality | Contrast stays gated |
-| **Time-of-day pair** | Auto light/dark (e.g. summer-day ↔ summer-night) from schedule | Still one theme engine |
+| **Time-of-day pair** ✓ | Auto light/dark (e.g. summer-day ↔ summer-night) from schedule | ✓ shipped #79 (2026-07-10) — `settings.autoTheme` + timer; still one engine |
 | **Theme switch speed** | Wallpapers artifact split (LATER) if switches still feel slow | GOALS: no second pipeline |
 
 ---