refactor(tui): extract Activity readout and show local time

Move activity data assembly out of tui.py into activity_readout, behind
readout(conn, selection, now). Dashboard and fenris-monitor enable now show
local time with a timezone label, inspected points keep a secondary UTC line,
and the legacy UTC-relabelled day and hour branches are gone. Time formatting
(including freshness_age_human) lives in timefmt. Hour offsets now render as
+05:30 to match day labels.

docs/spec/glint-dashboard-design.md

@@ -95,9 +95,10 @@ finance, email, or gallery features.
   reference does not require squeezing its entire density into small terminals.
 
 These defaults implement the confirmed choices. Date entry and inspection
-retain existing evidence precision: hourly/daily UTC evidence is labelled UTC,
-while local-day totals keep their recorded timezone. This visual redesign does
-not manufacture finer or local-hour precision from coarse UTC evidence.
+retain existing evidence precision: every time is shown in local time with its
+timezone label and a secondary UTC line on inspection, daily bars read
+local-day evidence, and local-day totals keep their recorded timezone. This
+visual redesign does not manufacture finer precision than the evidence holds.
 
 ## Smallest sufficient implementation proof