fix(telemetry): widen plan-presentation exposure event variant type to 5 variants (#50318)

<!-- ccr-slack-attribution -->
_Requested by **Pam Chia** · [Slack
thread](https://supabase.slack.com/archives/C076KTY11DF/p1789349119093319?thread_ts=1789349119.093319&cid=C076KTY11DF)_

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES

## What kind of change does this PR introduce?

Bug fix (telemetry type).

## What is the current behavior?

The `pricing_panel_plan_presentation_experiment_exposed` event's
`variant` property in `packages/common/telemetry-constants.ts` only
types 3 of the experiment's 5 live variants (`'control' | 'parity' |
'gaps'`), even though the experiment source in `plan-presentation.ts`
defines and actively uses 5: `control`, `parity`, `gaps`, `fullscreen`,
`fullscreen-gaps`. The two full-screen variants are silently untyped in
the telemetry catalog.

## What is the new behavior?

The `variant` property is widened to `'control' | 'parity' | 'gaps' |
'fullscreen' | 'fullscreen-gaps'`, matching the exact casing of
`PLAN_PRESENTATION_VARIANTS` in the experiment source, and consistent
with how other experiment-variant unions in the same file (e.g.
`rlsOptionVariant`) are kept in sync with their source enum.

## Additional context

Linear: GROWTH-1234

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01Gxb4n5ujMPeio1VmkowHc5

---
_Generated by [Claude
Code](https://claude.ai/code/session_01Gxb4n5ujMPeio1VmkowHc5)_

Co-authored-by: Claude <noreply@anthropic.com>

packages/common/telemetry-constants.ts

@@ -3622,7 +3622,7 @@ export interface PricingPanelPlanPresentationExperimentExposedEvent {
   action: 'pricing_panel_plan_presentation_experiment_exposed'
   properties: {
     /** The experiment variant the user is enrolled in */
-    variant: 'control' | 'parity' | 'gaps'
+    variant: 'control' | 'parity' | 'gaps' | 'fullscreen' | 'fullscreen-gaps'
   }
   groups: Omit<TelemetryGroups, 'project'>
 }