feat: upload test record attachments per run case

Allow testers to attach evidence files to a single test case within a
specific test run, proving the test was actually executed. Attachments
are scoped to the RunCase (per-execution), not the shared case definition.

Backend:
- runCaseAttachments join table + model (CASCADE on runCase/attachment)
- POST/GET /runcaseattachments routes (reuse /attachments download+delete)

Frontend:
- new "Test record" tab in the run case detail pane with drag-and-drop
  upload, scoped to reporters; i18n for all 6 locales

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

backend/migrations/20260624000000-create-runcase-attachments.js

@@ -0,0 +1,43 @@
+export async function up(queryInterface, Sequelize) {
+  await queryInterface.createTable('runCaseAttachments', {
+    id: {
+      type: Sequelize.INTEGER,
+      primaryKey: true,
+      autoIncrement: true,
+    },
+    runCaseId: {
+      type: Sequelize.INTEGER,
+      references: {
+        model: 'runCases',
+        key: 'id',
+      },
+      onUpdate: 'CASCADE',
+      onDelete: 'CASCADE',
+    },
+    attachmentId: {
+      type: Sequelize.INTEGER,
+      references: {
+        model: 'attachments',
+        key: 'id',
+      },
+      onUpdate: 'CASCADE',
+      onDelete: 'CASCADE',
+    },
+    createdAt: {
+      type: Sequelize.DATE,
+      allowNull: false,
+    },
+    updatedAt: {
+      type: Sequelize.DATE,
+      allowNull: false,
+    },
+  });
+
+  await queryInterface.addIndex('runCaseAttachments', ['runCaseId', 'attachmentId'], {
+    unique: true,
+  });
+}
+
+export async function down(queryInterface) {
+  await queryInterface.dropTable('runCaseAttachments');
+}