feat(relationship): editable relationships with LocalDate+DatePrecision dates and notes (#841)

Closes #837

Makes `PersonRelationship` fully editable (type, related person, dates, notes), migrates its dates from `Integer fromYear/toYear` to `LocalDate + DatePrecision` (mirroring the #773 person pattern, ADR-039 / V76), activates the previously-dead `notes` column, and gives the Zeitstrahl's derived **Heirat** events full date precision for free.

Both Open Decisions confirmed as adopted: **no `@Version`** (last-write-wins, single-writer archive) and **`DELETE` ownership-mismatch aligned 403 → 404** (anti-enumeration, matching the new `PUT`).

## What's in it
- **V78** migrates `person_relationships.from_year/to_year` → `from_date`/`to_date` + NOT-NULL `*_date_precision` (default `UNKNOWN`); pre-check abort on corrupt years, `YYYY-01-01`/`YEAR` backfill, 5 named CHECK constraints, year columns dropped.
- **`PUT /api/persons/{id}/relationships/{relId}`** (`@RequirePermission(WRITE_ALL)`) re-runs every create invariant (self / coherence / order / reverse-PARENT_OF / duplicate) and re-flags family membership; orientation preserved per viewpoint.
- New `ErrorCode.INVALID_RELATIONSHIP_DATES` registered in all four sites (§3.6).
- `TimelineEventService` sources the derived marriage date from `SPOUSE_OF.fromDate` + precision.
- Frontend: `RelationshipDateField` (DAY/MONTH/YEAR), upsert-capable `AddRelationshipForm` (pre-fill + notes + in-flight submit lock), `RelationshipChip` Edit affordance, `updateRelationship` server action, read-view date range + notes, `formatRelationshipDateRange` helper. `api.ts` regenerated.
- Docs: ADR-044, db-orm/db-relationships diagrams, DEPLOYMENT §5 deploy note, RTM REQ-001…REQ-019.

## Requirements
All 19 EARS requirements implemented red/green and marked `Done` in `.specify/rtm.md`.

## Test plan
- **Backend** (targeted, green): `RelationshipMigrationTest` (Testcontainers pg16, 8), `RelationshipServiceTest` (22), `RelationshipControllerTest` (15), `RelationshipServiceIntegrationTest` (real DB, 10), `DerivedEventsAssemblyTest` (17), `ArchitectureTest` (14); `clean package` builds.
- **Frontend** (green): `relationshipDates.spec.ts`, `AddRelationshipForm.svelte.spec.ts`, `RelationshipChip.svelte.spec.ts`, `PersonRelationshipsCard.svelte.test.ts`, `page.server.spec.ts`, `messages.spec.ts`. `npm run check` = 798 (below the ~834 baseline); `npm run lint` clean.

## Notes for reviewers
- **Spec deviation:** the edit form was built by making `AddRelationshipForm` upsert-capable rather than a duplicate `EditRelationshipForm` (DRY); RTM rows reference `AddRelationshipForm.svelte.spec.ts`.
- `api.ts` regenerated from the live spec; only relationship-relevant hunks remain (one springdoc `PageableObject` field-reorder pruned).
- **Deploy:** V78 is one-way and not rolling-deploy-safe — stop old JAR → start new JAR (Flyway runs first); targeted `pg_restore -t person_relationships` for rollback. No maintenance window.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Marcel <marcel@familienarchiv>
Reviewed-on: #841

frontend/src/lib/person/relationship/RelationshipDateField.svelte

@@ -0,0 +1,38 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+import DateInputWithPrecision from '$lib/shared/primitives/DateInputWithPrecision.svelte';
+import type { DatePrecision } from '$lib/shared/utils/documentDate';
+
+// Only DAY / MONTH / YEAR are offered (same as the person life-date field and the
+// 60+ author audience). Storage still accepts all seven precisions; SEASON/RANGE/
+// APPROX render correctly elsewhere but make no sense to enter for a relationship.
+let {
+	name,
+	legend,
+	initialIso = '',
+	initialPrecision = null
+}: {
+	name: string;
+	legend: string;
+	initialIso?: string | null;
+	initialPrecision?: string | null;
+} = $props();
+
+const precisions: { value: DatePrecision; label: string }[] = $derived([
+	{ value: 'DAY', label: m.relation_precision_day() },
+	{ value: 'MONTH', label: m.relation_precision_month() },
+	{ value: 'YEAR', label: m.relation_precision_year() }
+]);
+</script>
+
+<DateInputWithPrecision
+	name={name}
+	legend={legend}
+	precisionLabel={m.relation_label_date_precision()}
+	precisions={precisions}
+	hint={m.relation_date_placeholder_hint()}
+	initialIso={initialIso}
+	initialPrecision={initialPrecision}
+	inputClass="bg-surface"
+	selectClass="bg-surface text-ink-3"
+/>