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.

tests/test_live_graph.py

@@ -18,12 +18,9 @@ from fenris.activity_selection import IntervalIdentity
 from fenris.monitoring_periods import ensure_period_open
 from fenris.status import ACCURACY_SEC, CADENCE_DEFAULT_S, FRESH_THRESHOLD_S
 from fenris.store import init_store
-from fenris.tui import (
-    LIVE_WINDOW_H,
-    FenrisTuiApp,
-    LiveActivityGraph,
-    _query_live_graph_data,
-)
+from fenris.timefmt import local_clock, tz_label, utc_range_label
+from fenris.activity_readout import LIVE_WINDOW_H, _query_live_graph_data
+from fenris.tui import FenrisTuiApp, LiveActivityGraph
 
 # ---------------------------------------------------------------------------
 # Helpers
@@ -70,8 +67,10 @@ def _live_intervals(count=4):
         intervals.append({
             "start_ts": start.isoformat(),
             "end_ts": end.isoformat(),
-            "start_label": start.strftime("%H:%M"),
-            "end_label": end.strftime("%H:%M"),
+            "start_label": local_clock(start, "UTC"),
+            "end_label": local_clock(end, "UTC"),
+            "timezone_label": tz_label(end, "UTC"),
+            "utc_label": utc_range_label(start, end),
             "bytes_written": (index + 1) * 1000,
             "bytes_read": (index + 1) * 500,
             "elapsed_s": 180,