Add time-based screen scheduling (e.g. Journey every morning 6-8)

New "Time-based schedule" section on the Rotation settings page: up to
4 rules, each a screen + a daily HH:MM-HH:MM window (crossing midnight
is fine, e.g. 22:00-02:00). While a rule's window is active, that
screen overrides rotation and any manual pin -- without touching
either's underlying state, so things go back to exactly how they were
once the window ends. Navidrome-playing still wins on top of a
schedule rule, same as it already does over everything else.

config.py: new schedules list (get_schedules/set_schedules), each rule
just {screen_id, start, end} -- being in the list *is* being enabled,
no separate flag (a settings row is "disabled" by leaving its screen
dropdown on "-- none --").

scheduler.py: _time_in_window() handles same-day and midnight-wrapping
windows, treats a zero-width window as never-matching (more likely a
blank settings row than an intentional all-day rule).
_active_scheduled_screen() slots into _select_screen() between
Navidrome-priority and the pin/rotation fallback.

Verified: unit tests for _time_in_window's edge cases (wraparound,
zero-width, malformed input) and the priority override, plus an
end-to-end run against the real app -- pinned a screen, added a rule
active right now, confirmed the status page switched to the scheduled
screen within one tick.

web/templates/base.html

@@ -99,7 +99,7 @@
     label { display: block; font-weight: 600; margin-bottom: 0.35rem; font-size: 0.85rem; }
     .hint { font-size: 0.78rem; color: var(--text-muted); margin: 0.35rem 0 0; }
 
-    input[type=text], input[type=password], input[type=number], select, input[type=file] {
+    input[type=text], input[type=password], input[type=number], input[type=time], select, input[type=file] {
       width: 100%;
       padding: 0.6rem 0.7rem;
       font-size: 0.95rem;