Function isDemoMode

isDemoMode(
userOrTeamSlug: string | null | undefined,
campaignSlug: string | null | undefined,
): boolean
Match a (user-or-team slug, campaign slug) pair against the demo identifiers. Mirrors the legacy playlive-overlay-data-layer predicate verbatim so downstream behavior is byte-equal.

Callers pass already-sigil-stripped slugs.
Parameters
- userOrTeamSlug: string | null | undefined
- campaignSlug: string | null | undefined
Returns boolean
Example
```
isDemoMode("playliveDemoUser", "playliveDemoCampaign"); // true
isDemoMode("playliveDemoTeam", null);                   // true (team-only)
```
- Defined in fundraiser-data/src/demo/index.ts:105