Add design artifacts for view event feature (007)

Spec, research, data model, API contract, implementation plan, and
task breakdown for the public event detail page.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/007-view-event/data-model.md

@@ -0,0 +1,56 @@
+# Data Model: View Event Landing Page (007)
+
+**Date**: 2026-03-06
+
+## Entities
+
+### Event (modified — adds `timezone` field)
+
+| Field           | Type             | Required | Constraints              | Notes                            |
+|-----------------|------------------|----------|--------------------------|----------------------------------|
+| id              | Long             | yes      | BIGSERIAL, PK            | Internal only, never exposed     |
+| eventToken      | UUID             | yes      | UNIQUE, NOT NULL         | Public identifier in URLs        |
+| organizerToken  | UUID             | yes      | UNIQUE, NOT NULL         | Secret, never in public API      |
+| title           | String           | yes      | 1–200 chars              |                                  |
+| description     | String           | no       | max 2000 chars           |                                  |
+| dateTime        | OffsetDateTime   | yes      |                          | Organizer's original offset      |
+| timezone        | String           | yes      | IANA zone ID, max 64     | **NEW** — e.g. "Europe/Berlin"   |
+| location        | String           | no       | max 500 chars            |                                  |
+| expiryDate      | LocalDate        | yes      | Must be future at create | Auto-deletion trigger            |
+| createdAt       | OffsetDateTime   | yes      | Server-generated         |                                  |
+
+**Validation rules**:
+- `timezone` must be a valid IANA zone ID (`ZoneId.getAvailableZoneIds()`).
+- `expiryDate` must be in the future at creation time (existing rule).
+
+**State transitions**:
+- Active → Expired: when `expiryDate < today` (computed, not stored).
+- Active → Cancelled: future (US-18), adds `cancelledAt` + `cancellationMessage`.
+
+### RSVP (future — not created in this feature)
+
+Documented here for context only. Created when the RSVP feature (US-8+) is implemented.
+
+| Field      | Type    | Required | Constraints                  |
+|------------|---------|----------|------------------------------|
+| id         | Long    | yes      | BIGSERIAL, PK                |
+| eventId    | Long    | yes      | FK → events.id               |
+| guestName  | String  | yes      | 1–100 chars                  |
+| attending  | Boolean | yes      | true = attending             |
+| createdAt  | OffsetDateTime | yes | Server-generated           |
+
+## Relationships
+
+```
+Event 1 ←── * RSVP (future)
+```
+
+## Type Mapping (full stack)
+
+| Concept      | Java              | PostgreSQL    | OpenAPI             | TypeScript |
+|--------------|-------------------|---------------|---------------------|------------|
+| Event time   | `OffsetDateTime`  | `timestamptz` | `string` `date-time`| `string`   |
+| Timezone     | `String`          | `varchar(64)` | `string`            | `string`   |
+| Expiry date  | `LocalDate`       | `date`        | `string` `date`     | `string`   |
+| Token        | `UUID`            | `uuid`        | `string` `uuid`     | `string`   |
+| Count        | `int`             | `integer`     | `integer`           | `number`   |