feat(identities): full-text search for identity popover switcher backed by DB

[coderabbitai]

Problem

The identity popover switcher in the breadcrumb navigation (IdentityCrumb) currently uses trpc.identity.query.useQuery({}) which is paginated with a server-side default of limit: 50. This means:

1. Workspaces with more than 50 identities will have results silently truncated.
2. The in-popover search is client-side only — identities outside the first page cannot be found.

Currently, the only available search is described as an "AI search" which does not provide reliable full-text search across the entire identities collection in the database.

Proposed Solution

Implement full-text search for the identity popover switcher that:

• Queries the database directly (not just client-side filtering of a capped result set)
• Wires the popover search input through to the trpc search input parameter so all matching identities are returned regardless of pagination

This would bring the identity switcher in line with the reliability expected from the project/namespace crumb switchers.

References

• PR: feat(dashboard): context-aware breadcrumb #6193
• Comment: feat(dashboard): context-aware breadcrumb #6193 (comment)

Raised by @chronark

[linear-code]

ENG-2809