Fix agent_profile_switched telemetry event name (#57739)

The `agent_profile_switched` event fired from the profile picker was
using snake_case instead of the title case used by every other agent
telemetry event. This caused it to land in Amplitude as a separate event
from the `Agent Profile Switched` event fired by keyboard cycling,
making it impossible to track profile switches in a single chart.

Renames the event to `Agent Profile Switched` to match. The `source`
property (`"picker"` vs `"cycle"`) still distinguishes the two code
paths.

Release Notes:

- N/A

crates/agent_ui/src/profile_selector.rs

@@ -541,7 +541,7 @@ impl PickerDelegate for ProfilePickerDelegate {
                     provider.set_profile(profile_id.clone(), cx);
 
                     telemetry::event!(
-                        "agent_profile_switched",
+                        "Agent Profile Switched",
                         profile_id = profile_id.as_str(),
                         source = "picker"
                     );