feat: add per-event custom logo upload with bug fixes

Add event-level custom logo upload/delete endpoints and UI, allowing
per-event logos to override the global branding logo in gallery views.

Also fixes several bugs discovered during testing:
- fix: category_id 'individual' parsed as NaN causing photo upload failures
- fix: gallery auth race condition where photos query fired before token stored
- fix: gallery-photos query not invalidated after favorite/like mutations
- fix: e2e test race conditions with View Gallery button detachment

backend/migrations/core/063_add_event_custom_logo.js

@@ -0,0 +1,53 @@
+/**
+ * Migration: Add custom logo support to events table
+ *
+ * Allows per-event custom logo that overrides the global branding logo:
+ * - hero_logo_url: Public path to the uploaded custom logo
+ * - hero_logo_path: Full filesystem path to the custom logo
+ *
+ * Logo priority: Event custom logo > Global branding logo > Default PicPeak logo
+ *
+ * Addresses GitHub Issue #138: Per-event custom logo option
+ */
+
+exports.up = async function (knex) {
+  console.log('Adding custom logo columns to events table...');
+
+  const hasUrlColumn = await knex.schema.hasColumn('events', 'hero_logo_url');
+  if (!hasUrlColumn) {
+    await knex.schema.table('events', (table) => {
+      table.string('hero_logo_url', 500).nullable().defaultTo(null);
+    });
+    console.log('Added hero_logo_url column');
+  }
+
+  const hasPathColumn = await knex.schema.hasColumn('events', 'hero_logo_path');
+  if (!hasPathColumn) {
+    await knex.schema.table('events', (table) => {
+      table.string('hero_logo_path', 500).nullable().defaultTo(null);
+    });
+    console.log('Added hero_logo_path column');
+  }
+
+  console.log('Migration 063_add_event_custom_logo completed successfully');
+};
+
+exports.down = async function (knex) {
+  console.log('Rolling back custom logo columns...');
+
+  const hasUrlColumn = await knex.schema.hasColumn('events', 'hero_logo_url');
+  if (hasUrlColumn) {
+    await knex.schema.table('events', (table) => {
+      table.dropColumn('hero_logo_url');
+    });
+  }
+
+  const hasPathColumn = await knex.schema.hasColumn('events', 'hero_logo_path');
+  if (hasPathColumn) {
+    await knex.schema.table('events', (table) => {
+      table.dropColumn('hero_logo_path');
+    });
+  }
+
+  console.log('Custom logo columns dropped');
+};