Show trustworthy local-day activity totals (#90)

Add local-day activity summaries derived from UTC hour observations using
the system timezone, with durable storage in a new local_days table.
The collector derives local-day read/write totals after UTC aggregation;
the TUI displays them with timezone, completeness state, and coverage.

Schema: bump SCHEMA_VERSION to 3, add local_days table (migration 2→3
is pure addition, idempotent, preserves newer-schema refusal).

src/fenris/collector.py

@@ -345,6 +345,20 @@ def run_collection(
                 from .day_aggregate import derive_all_days, persist_day_aggregate
                 for agg in derive_all_days(conn):
                     persist_day_aggregate(conn, agg)
+
+                # Derive local-day summary using system timezone (issue #90)
+                try:
+                    from .tz_util import detect_system_tz
+                    from .local_day import derive_local_day_summary, persist_local_day
+                    tz_name = detect_system_tz()
+                    clock_now = clock.utcnow()
+                    local_summary = derive_local_day_summary(conn, tz_name, clock_now)
+                    if local_summary is not None:
+                        persist_local_day(conn, local_summary)
+                except Exception:
+                    # Local-day derivation failure must not prevent publication
+                    pass
+
                 conn.commit()
             except Exception:
                 # Derivation failure must not prevent sample persistence (issue #73 AC6)