Enhance Managed Auth documentation by updating health check intervals…

[masnwilliams]

Note

Low Risk
Documentation-only updates that clarify plan limits and Managed Auth timeout semantics; no production logic changes.

Overview
Updates Managed Auth documentation to clarify plan-based health check interval limits (Hobbyist 1h, Startup 15m, Enterprise 5m), including adding this limit to the Pricing & Limits concurrency table and expanding the billing section with guidance on cost/usage impact.

Also updates Hosted UI/Programmatic flow docs to reflect longer session/flow timeouts (10 minutes waiting for user input, 20 minutes overall) and adjusts FAQ billing language to note that lower intervals increase browser usage.

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