fix: restore dashboard history and complete activity calendar

Combine retained daily aggregates with recent usage without replaying historical records or changing the activation boundary. Complete activation-day metrics and expose the UTC calendar used by legacy history.

Render all 365 calendar dates, size heatmap cells responsively, and soften cell corners. Add regression coverage for history cutoffs, retention, sparse dates, and timezone boundaries.

crates/aether-data/runtime/schema/README.md

@@ -157,6 +157,22 @@ The statistics schema migrations above do not embed a historical data rebuild.
 The new dashboard's activation boundary is not moved by legacy backfills, so
 they do not restore pre-activation dashboard totals.
 
+For upgraded installations that retain historical `stats_daily` rows and a
+`stats_summary` cutoff, the homepage has a read-only compatibility path. Lifetime
+totals and activity combine daily aggregates strictly before that cutoff with
+recent usage at or after it, in one database snapshot. This preserves history
+whose individual requests have already expired and avoids double counting when
+daily aggregation advances the cutoff. These activity dates use UTC, matching
+the historical aggregates; the API reports `activity_timezone` separately from
+the timezone used for today's metrics. On the activation day, today's metrics
+also include requests before activation, with active users deduplicated across
+the boundary. The stored activation timestamp and source records are unchanged.
+
+This compatibility path retains the legacy daily-aggregation retention contract:
+unaggregated recent usage must remain available until the daily cutoff advances.
+Installations without historical daily aggregates continue to read the durable
+incremental dashboard projection.
+
 Deleted users are excluded from dashboard active-user reads even when an older
 version left orphan activity rows. The anonymization upgrade installs rules for
 future deletions without cleaning old rows during migration; those old activity

crates/aether-data/runtime/src/repository/usage/memory/dashboard_summary.rs

@@ -212,6 +212,7 @@ impl InMemoryUsageReadRepository {
             stats_since: projection.since.to_rfc3339(),
             generated_at: now.to_rfc3339(),
             timezone: query.timezone.clone(),
+            activity_timezone: query.timezone.clone(),
             today_from: today_from.to_rfc3339(),
             window_seconds: (now - today_from).num_milliseconds().max(0) as f64 / 1000.0,
             today,