Simple Activity Logging

All four partner organisations name simple activity registration as their #1 priority and describe today's situation as untenable - one HLF peer mentor logged 380 separate registrations in a year. Removing friction directly attacks the root cause of underreporting, which in turn drives the Bufdir funding case for every tenant. Strategically, this is the single feature that justifies the whole mobile product: every other capability (statistics, expense, gamification) is downstream of activities actually being logged. Adoption hinges on the "under two clicks" promise from the NHF workshop.

Flutter screen backed by Riverpod state and Drift offline-first persistence; writes go to the sync outbox so logging works offline and reconciles when connectivity returns. Default values (current date, 30-minute duration) are pre-filled and editable. Optimistic UI with rollback on sync failure. Activity records flow into the same `activities` table consumed by statistics, Bufdir export, and admin oversight, so schema fidelity matters more than UI polish. WCAG 2.2 AA target-size and contrast tokens applied via the design token system. No expense or attachment coupling at this layer - those are separate toggleable modules.