Add GET /events/{token} endpoint and timezone field to OpenAPI spec

OpenAPI: new GetEventResponse schema, timezone on Create request/response.
Liquibase: add timezone VARCHAR(64) NOT NULL DEFAULT 'UTC' column.

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

backend/src/main/resources/db/changelog/002-add-timezone-column.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<databaseChangeLog
+    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
+        http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
+
+    <changeSet id="002-add-timezone-column" author="fete">
+        <addColumn tableName="events">
+            <column name="timezone" type="varchar(64)" defaultValue="UTC">
+                <constraints nullable="false"/>
+            </column>
+        </addColumn>
+    </changeSet>
+
+</databaseChangeLog>

backend/src/main/resources/db/changelog/db.changelog-master.xml

@@ -7,5 +7,6 @@
 
     <include file="db/changelog/000-baseline.xml"/>
     <include file="db/changelog/001-create-events-table.xml"/>
+    <include file="db/changelog/002-add-timezone-column.xml"/>
 
 </databaseChangeLog>

backend/src/main/resources/openapi/api.yaml

@@ -37,6 +37,34 @@ paths:
               schema:
                 $ref: "#/components/schemas/ValidationProblemDetail"
 
+  /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:
     CreateEventRequest:
@@ -44,6 +72,7 @@ components:
       required:
         - title
         - dateTime
+        - timezone
         - expiryDate
       properties:
         title:
@@ -58,6 +87,10 @@ components:
           format: date-time
           description: Event date and time with UTC offset (ISO 8601)
           example: "2026-03-15T20:00:00+01:00"
+        timezone:
+          type: string
+          description: IANA timezone of the organizer
+          example: "Europe/Berlin"
         location:
           type: string
           maxLength: 500
@@ -74,6 +107,7 @@ components:
         - organizerToken
         - title
         - dateTime
+        - timezone
         - expiryDate
       properties:
         eventToken:
@@ -93,11 +127,61 @@ components:
           type: string
           format: date-time
           example: "2026-03-15T20:00:00+01:00"
+        timezone:
+          type: string
+          description: IANA timezone of the organizer
+          example: "Europe/Berlin"
         expiryDate:
           type: string
           format: date
           example: "2026-06-15"
 
+    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
+
     ProblemDetail:
       type: object
       properties: