#16811: Fix Telnyx inbound calls silently dropped — normalizeEvent missing direction/from/to

Stumbled on this while looking at #16601. The Telnyx provider's `normalizeEvent` never passes `direction`, `from`, or `to` from the webhook payload into the normalized event. Without `direction: "inbound"`, `processEvent` can't tell it's an incoming call and just drops it. Twilio already does this correctly (via `parseDirection`), so I followed the same pattern — added a static `parseDirection` helper that maps Telnyx's `incoming`/`outgoing` to the normalized `inbound`/`outbound` format, and put all three fields on `baseEvent` so every event type gets them. Tests added for both inbound and outbound direction mapping through `parseWebhookEvent`. Fixes #16601 <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixes a bug where Telnyx inbound calls were silently dropped because `normalizeEvent` never populated the `direction`, `from`, or `to` fields on the normalized event. Without `direction: "inbound"`, `processEvent` in `events.ts` couldn't identify the call as inbound and would skip creating a call record for it. - Adds a `parseDirection` static method to `TelnyxProvider` that maps Telnyx's `"incoming"`/`"outgoing"` values to the normalized `"inbound"`/`"outbound"` format (mirrors the existing pattern in the Twilio and Plivo providers) - Populates `direction`, `from`, and `to` on `baseEvent` so all Telnyx event types carry these fields - Adds tests covering inbound direction, outbound direction, and missing direction scenarios <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it fixes a clear bug with a well-scoped, pattern-consistent change. - The change is minimal and targeted: it adds three fields to the base event object and a pure static helper method. It follows the exact same pattern already established by the Twilio and Plivo providers. The fix is necessary — without it, inbound Telnyx calls are silently dropped because processEvent cannot identify them. Tests cover inbound, outbound, and missing direction cases. No security implications, no breaking changes. - No files require special attention. _{Last reviewed commit: 97e21d2} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->