Show the live time on the set-clock page instead of a stale cached value

[bob9]

Summary

The set-clock page's rollers are populated from a value cached in memory, not from the RTC. If the clock changes behind the scenes — the goggles already accept MSP_SET_RTC from the ELRS backpack today — the page keeps showing the stale time, and a pilot who opens it and hits save writes that stale time back over the correct one.

Why it helps pilots: the clock page becomes trustworthy. What it shows is the actual current time, so pilots can confirm at a glance that their clock (and therefore their DVR timestamps) is right, and can't accidentally undo an automatic time sync by saving old roller values.

Implementation

Changes confined to src/ui/page_clock.c:

• On page entry, re-read the RTC before building the rollers, so they always start at the actual current time instead of the value cached at boot or the last manual set.
• The refresh is driven from the page's on_update hook (rather than an lvgl timer scoped to enter/exit), so the page is already showing the live time when the user merely scrolls onto the Clock menu item — no need to enter the page. Paced with the lvgl tick, since the menu loop's delta_ms resets its reference on every call.
• The rollers track the live clock once a second — but never fighting the user: the refresh pauses while a roller is open or an edit is unsaved, backs off for 3 seconds after any dial/click input, and only rebuilds a roller's option list when its contents actually change (a year/month rollover changes the day count) — otherwise it just moves the selected indices.

No change to how the clock is set or saved.

Related PRs

Standalone — useful with the existing backpack MSP_SET_RTC path alone — but it pairs naturally with the automatic time-sync set, which makes background clock updates much more common:

• Send RTC time from the TX backpack to the VRX backpack over ESP-NOW ExpressLRS/Backpack#231 — TX backpack distributes the time to the VRX backpack and goggles.
• Automatically sync backpack time from the handset (real timestamps on goggle DVR) + lua memory optimisations ExpressLRS/Lua-Scripts#18 and Send handset time to the TX backpack to set its RTC ExpressLRS/ExpressLRS#3701 — one-press time sync from the handset.