refactor: rename eventstream -> activity, cycles -> period

eventstream was confusingly branded "Events" in the app registry,
colliding with the real events calendar module. Renamed to activity
(DE: Aktivität) since it's a live activity feed across all modules.

cycles -> period (DE: Periode) makes the menstrual-tracking module
self-describing. Tables cycles/cycleDayLogs/cycleSymptoms renamed to
periods/periodDayLogs/periodSymptoms; field cycleId -> periodId;
TimeBlockType 'cycle' -> 'period'; domain event CycleDayLogged ->
PeriodDayLogged. Generic "cycle" usages (billing, lifecycle, breath,
bicycle, import cycles) left untouched.

Constant disambiguation: prior DEFAULT_PERIOD_LENGTH (bleeding days)
renamed to DEFAULT_BLEEDING_DAYS; prior DEFAULT_CYCLE_LENGTH (28d full
cycle) is now DEFAULT_PERIOD_LENGTH.

Pre-launch, no data migration needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/prometheus/prometheus.yml

@@ -247,7 +247,7 @@ scrape_configs:
           - https://mana.how/journal
           - https://mana.how/dreams
           - https://mana.how/firsts
-          - https://mana.how/cycles
+          - https://mana.how/period
           - https://mana.how/events
           - https://mana.how/finance
           - https://mana.how/places