Support configurable person display name format to include group/company properties (B2B use case)

Feature request

Is your feature request related to a problem?
PostHog displays person names (e.g. "First Last") across many surfaces – session replay list, person profiles, funnel breakdowns, activity logs, cohorts, and more. For B2B products, a person's name alone is rarely enough context. You need to know which business they belong to to make sense of the data. There is currently no way to configure a display format that includes company or group properties alongside the person's name.

Describe the solution you'd like
A project-level setting to configure a person display name template using person or group properties. For example:

Template: {firstName} {lastName} ({businessName})
Result: "Mo Khalil (Bella Booking)"
This should apply consistently everywhere a person's name is shown:

Session replay list
Person profiles and person modal
Funnel breakdowns
Cohort member lists
Activity logs
Any other surface that displays a person's identity
Describe alternatives you've considered
Setting $name to a composite string like "First Last (Business Name)" during posthog.identify() works as a workaround, but it pollutes the $name property globally, makes it harder to use name independently, and requires re-identifying users if the business name changes.

Additional context
This is a fundamental B2B product analytics need. When your users are employees of businesses, the business context is as important as the individual's name. Tools like Intercom, Salesforce, and others treat this as a first-class concept. PostHog's group analytics already models this relationship – surfacing it in person display names would make the whole product significantly more useful for B2B teams.

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

Start by tracing how person names are rendered in the session replay list, person profiles, funnel breakdowns, cohort member lists, and activity logs, then identify where project-level settings and group properties are handled. Done means a configurable person display template can include person and group properties and is applied consistently across the named identity surfaces.