docs(relationship): ADR-044, DB diagrams, deploy runbook, RTM rows

- ADR-044 extends ADR-039 to the relationship edge: LocalDate+DatePrecision,
  update re-validation of create invariants, no @Version (last-write-wins),
  DELETE→404 anti-enumeration alignment, precise derived marriage date, and the
  relationshipDates.ts location reusing the existing person→shared boundary.
- db-orm.puml: person_relationships now carries from_date/from_date_precision/
  to_date/to_date_precision; db-relationships.puml gets a V78 columns-only note.
- DEPLOYMENT.md §5: V78 deploy note — no maintenance window, stop-old-then-start
  ordering (not rolling-deploy-safe), targeted pg_restore rollback.
- CLAUDE.md error-code list gains INVALID_RELATIONSHIP_DATES.
- rtm.md: REQ-001..REQ-019 for #837 mapped to impl + tests, all Done.

Refs #837
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/architecture/db/db-orm.puml

@@ -1,6 +1,6 @@
 @startuml db-orm
-' Schema source: Flyway V1–V77 (excl. V37, V43 — intentionally removed)
-' Schema as of:  V77 (2026-06-12)
+' Schema source: Flyway V1–V78 (excl. V37, V43 — intentionally removed)
+' Schema as of:  V78 (2026-06-14)
 ' ⚠ This is a versioned snapshot. Update when the schema changes significantly.
 
 hide circle
@@ -211,8 +211,10 @@ package "Persons" {
     person_id : UUID <<FK>>
     related_person_id : UUID <<FK>>
     relation_type : VARCHAR(30) NOT NULL
-    from_year : INTEGER
-    to_year : INTEGER
+    from_date : DATE
+    from_date_precision : VARCHAR(16) NOT NULL DEFAULT 'UNKNOWN'
+    to_date : DATE
+    to_date_precision : VARCHAR(16) NOT NULL DEFAULT 'UNKNOWN'
     notes : VARCHAR(2000)
     created_at : TIMESTAMPTZ NOT NULL
   }