fix(events): NaN from slideshow seed breaks event creation on PostgreSQL

The create route seeds show_interval_ms/show_transition_ms from
app_settings through an inline guard that pre-checked Number.isFinite(+v)
but then used parseInt(v). The two disagree for null/''/true — +null is 0
(finite) while parseInt(null) is NaN — so when the slideshow settings rows
are absent (getAppSetting returns its null default), NaN flowed through
Math.min/Math.max into the INSERT. PostgreSQL rejects NaN for integer
columns; SQLite silently stores NULL, which is why every SQLite-based
test passed while POST /api/admin/events 500'd on the PG dev stack and
broke the e2e smoke suite.

Fix: parse first, then check — clampIntOrUndefined in utils/numericHelpers
(unit-tested against every failure-mode input). Verified end-to-end: the
previously-failing minimal create now succeeds against the PG dev stack.

backend/src/routes/adminEvents.js

@@ -27,6 +27,7 @@ const { validateFileType } = require('../utils/fileSecurityUtils');
 const { requireEventOwnership } = require('../middleware/ownership');
 const { requireFeatureFlag } = require('../middleware/requireFeatureFlag');
 const { getAppSetting } = require('../utils/appSettings');
+const { clampIntOrUndefined } = require('../utils/numericHelpers');
 const { getFrontendBaseUrl } = require('../utils/frontendUrl');
 const downloadZipService = require('../services/downloadZipService');
 
@@ -682,7 +683,13 @@ router.post('/', adminAuth, requirePermission('events.create'), [
     let slideshowSeed = {};
     if (await hasColumnCached('events', 'show_interval_ms')) {
       try {
-        const intP = (v, min, max) => (Number.isFinite(+v) ? Math.min(max, Math.max(min, parseInt(v, 10))) : undefined);
+        // parseInt-first: the previous `Number.isFinite(+v)` pre-check let
+        // NaN through for null/''/true (+null is 0, parseInt(null) is NaN),
+        // producing show_interval_ms=NaN in the INSERT — PG rejects that
+        // with "invalid input syntax for type integer" while SQLite
+        // silently stores NULL, so event creation 500'd on PG whenever the
+        // slideshow app_settings rows were absent.
+        const intP = (v, min, max) => clampIntOrUndefined(v, min, max);
         const oneOf = (v, allowed) => (allowed.includes(v) ? v : undefined);
         const i = intP(await getAppSetting('slideshow_interval_ms', undefined), 1000, 120000);
         const tr = oneOf(await getAppSetting('slideshow_transition', undefined), SLIDESHOW_TRANSITIONS);