feat(fleet): live mode wiring the UI to the manager

[Bugs5382]

Summary

Add a VITE_FLEET_MODE (mock | live | live-auth) data-source seam so the Fleet Manager UI can display live data from the manager backend. Wire all surfaces (nodes, certs, profiles, adapters, audit, enrollment) read-only in live mode; mock stays the default and is unchanged.

Acceptance criteria

• VITE_FLEET_MODE seam; mock is the default (existing behavior unchanged).
• All surfaces render live from the manager; CSP allows the manager origin; no cold-load crash.
• Writes remain deferred (read-only).

Notes

Depends on the api + manager PRs.