docs: relabel UX restructure epic as EPIC-21 (#2190)
The UX restructure pages added in 4f2e67c used EPIC-19, which already names Backup & Restore.
Existing Backup & Restore EPIC-19 references are unchanged.
Co-Authored-By: Claude product-architect <noreply@anthropic.com>
docs: EPIC-19 UX restructure architecture (ADR-038..040, route map, planned API contracts)
- ADR-038 Information Architecture v2: sidebar-only navigation, shared route map + NavConfig,
kept URLs with permanent vCard/iCal URLs, reachability and click-counting rules
- ADR-039 One Money Service: single Left to spend with strict verdict, percentage grants on
listed items, closed label registry, no schema change
- ADR-040 System Events: metadata v1 params, write-time de-dup incl. A->B->A, data-only backfill,
display collapse, delete nothing
- Route-Map page from routemap.json with owner decisions 2.0 #3/#24 applied
- API-Contract: 18 planned contracts (+2a) marked Planned - EPIC-19
- Deviation Log rows: Schema diary_entries (invoice_created, NULL metadata, invoice_deposit),
API-Contract sourceEntityType, ADR-014 autoReschedule persistence
Co-Authored-By: Claude product-architect <noreply@anthropic.com>