Add 'Registered for a conference' intent signal (#41919)

## Summary

- Adds `'Registered for a conference'` to the `intentSignal` `isIn`
array in three files:
- `website/api/helpers/salesforce/create-historical-event.js` — between
`'Signed up for Fleet event'` and `'Engaged with Fleetie at event'`
- `website/api/controllers/webhooks/receive-from-clay.js` — between
`'Signed up for Fleet event'` and `'Engaged with Fleetie at event'`
-
`website/api/helpers/salesforce/update-or-create-contact-and-account.js`
— added to the `isIn` array
- This replaces the incorrect approach in PR #41918, which added the
signal to the handbook markdown table instead of the code where intent
signals are validated.

---

Built for [Sam
Pfluger](https://fleetdm.slack.com/archives/D0AF8QFBVHB/p1773789580384389?thread_ts=1773788922.891409&cid=D0AF8QFBVHB)
by [Kilo for Slack](https://kilo.ai/features/slack-integration)

---------

Co-authored-by: kiloconnect[bot] <240665456+kiloconnect[bot]@users.noreply.github.com>
Co-authored-by: Sam Pfluger <108141731+Sampfluger88@users.noreply.github.com>

website/api/controllers/webhooks/receive-from-clay.js

@@ -62,6 +62,7 @@ module.exports = {
         'Fleet channel member in osquery Slack',
         'Implemented a trial key',
         'Signed up for Fleet event',
+        'Registered for a conference',
         'Engaged with Fleetie at event',
         'Attended a Fleet happy hour',
         'Stared the fleetdm/fleet repo on GitHub',
@@ -158,3 +159,4 @@ module.exports = {
 
 
 };
+

website/api/helpers/salesforce/create-historical-event.js

@@ -51,6 +51,7 @@ module.exports = {
         'Fleet channel member in osquery Slack',
         'Implemented a trial key',
         'Signed up for Fleet event',
+        'Registered for a conference',
         'Engaged with Fleetie at event',
         'Attended a Fleet happy hour',
         'Stared the fleetdm/fleet repo on GitHub',

website/api/helpers/salesforce/update-or-create-contact-and-account.js

@@ -61,6 +61,7 @@ module.exports = {
       type: 'string',
       isIn: [
         'Subscribed to the Fleet newsletter',
+        'Registered for a conference',
         // 'Signed up for a fleetdm.com account',//
         // 'Submitted the "Talk to us" form',
         // 'Submitted the "Send a message" form',
@@ -565,3 +566,4 @@ module.exports = {
 
 
 };
+