time_edit_field now cycles through 5 fields (hour/min/day/month/year)
via long-press CONFIRM. Up/down adjusts whichever field is focused,
with day clamped to Days_In_Month() when month/year changes, and
Clock_RecalcWeekday() called after every date edit so the weekday
label stays in sync. UI_UpdateSetTimeDigit() now also refreshes the
weekday abbreviation when editing day/month/year, since the computed
weekday can change independently of which digit was actually touched.
Save writes the full date+weekday via PCF8563_WriteDateTime(). Also
removes PCF8563_ReadTime()/WriteTime(), now unused since every caller
was updated to the DateTime variants directly.
PCF8563's second/minute/hour/day/weekday/month/year registers are
contiguous (0x02-0x08), so PCF8563_ReadDateTime() bursts all 7 bytes
in one transaction. PCF8563_ReadTime() becomes a thin wrapper that
discards the date fields. WriteTime() is kept as its own 3-byte-only
implementation (writing only sec/min/hour) rather than routed through
the new WriteDateTime(), since forcing it through a 7-byte write would
require synthesizing date values and risk corrupting the stored date;
WriteDateTime() is added as a separate full 7-byte write for callers
that actually have real date+weekday values to persist.
