Surface invalid JSON errors in the create/duplicate event modal

[morcen]

What was broken

On the Events index page, the "Create Event" / "Duplicate Event" modal (resources/js/Pages/Events/Index.vue) parsed the Payload and Schema textareas in a watch() callback:

watch(payloadText, (newValue) => {
    try {
        form.payload = newValue ? JSON.parse(newValue) : null
    } catch (e) {
        // Invalid JSON - will be handled by backend validation
    }
})

When JSON.parse threw, the catch block did nothing, so form.payload/form.schema silently retained their last successfully-parsed value. The comment's claim that "backend validation" would catch it was false — the invalid text was never sent anywhere, so the backend never saw it.

In practice: a user typing a Payload or Schema value with a JSON syntax error, then clicking Save, got a success response and redirect — but the stored payload/schema reflected stale (or null) data, not what they actually typed. Silent data loss with a false "success" signal.

This is the same class of bug already fixed on the event edit page in #223 — that fix only touched Edit.vue, leaving the create/duplicate modal in Index.vue with the original silent-catch bug.

What changed

Applied the same fix pattern used in #223 to Index.vue's create/duplicate modal:

• Added payloadJsonError / schemaJsonError reactive state.
• The watchers now set a descriptive error message when JSON.parse fails, instead of silently swallowing it, and clear the error (and null out the field) when the textarea is emptied.
• InputError next to each textarea now shows payloadJsonError || form.errors.payload (and the schema equivalent).
• The "Create" button is disabled while either field has a parse error, and saveEvent() bails out early if an error is present — so an Enter-triggered submit can't slip through either.
• closeModal() resets the new error state alongside the existing form/text resets.

Tests

• Added tests/Feature/DashboardEventCreateTest.php, covering that events.store persists the submitted payload/schema and rejects a duplicate event name for the same user.
• Extended tests/e2e/specs/events.spec.ts with a case mirroring the one added for the edit page in Surface invalid JSON errors on the event edit page instead of silently discarding them #223, verifying the Create button disables and an "Invalid JSON" error appears when the payload textarea contains broken JSON, and that fixing the JSON clears the error and re-enables the button.
• Ran the full suite (composer test): 252 passed, 1 pre-existing skip.

Fixes #98