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/contracts/get-event.yaml

@@ -0,0 +1,94 @@
+# OpenAPI contract addition for GET /events/{token}
+# To be merged into backend/src/main/resources/openapi/api.yaml
+
+paths:
+  /events/{token}:
+    get:
+      operationId: getEvent
+      summary: Get public event details by token
+      tags:
+        - events
+      parameters:
+        - name: token
+          in: path
+          required: true
+          schema:
+            type: string
+            format: uuid
+          description: Public event token
+      responses:
+        "200":
+          description: Event found
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/GetEventResponse"
+        "404":
+          description: Event not found
+          content:
+            application/problem+json:
+              schema:
+                $ref: "#/components/schemas/ProblemDetail"
+
+components:
+  schemas:
+    GetEventResponse:
+      type: object
+      required:
+        - eventToken
+        - title
+        - dateTime
+        - timezone
+        - attendeeCount
+        - expired
+      properties:
+        eventToken:
+          type: string
+          format: uuid
+          description: Public event token
+          example: "a1b2c3d4-e5f6-7890-abcd-ef1234567890"
+        title:
+          type: string
+          description: Event title
+          example: "Summer BBQ"
+        description:
+          type: string
+          description: Event description (absent if not set)
+          example: "Bring your own drinks!"
+        dateTime:
+          type: string
+          format: date-time
+          description: Event date/time with organizer's UTC offset
+          example: "2026-03-15T20:00:00+01:00"
+        timezone:
+          type: string
+          description: IANA timezone name of the organizer
+          example: "Europe/Berlin"
+        location:
+          type: string
+          description: Event location (absent if not set)
+          example: "Central Park, NYC"
+        attendeeCount:
+          type: integer
+          minimum: 0
+          description: Number of confirmed attendees (attending=true)
+          example: 12
+        expired:
+          type: boolean
+          description: Whether the event's expiry date has passed
+          example: false
+
+    # Modification to existing CreateEventRequest — add timezone field
+    # CreateEventRequest (additions):
+    #   timezone:
+    #     type: string
+    #     description: IANA timezone of the organizer
+    #     example: "Europe/Berlin"
+    #   (make required)
+
+    # Modification to existing CreateEventResponse — add timezone field
+    # CreateEventResponse (additions):
+    #   timezone:
+    #     type: string
+    #     description: IANA timezone of the organizer
+    #     example: "Europe/Berlin"