Extract IsSPOG and ResolveConfigType into libs/auth

[mihaimitrea-db]

Summary

• Extract the SPOG detection heuristic into a shared IsSPOG(cfg, accountID) predicate in libs/auth/config_type.go, replacing inline checks in both profiles.go and ToOAuthArgument.
• Extract ResolveConfigType(cfg) that wraps ConfigType() with SPOG-aware overrides, used by profiles.go.
• ToOAuthArgument now calls IsSPOG instead of duplicating the DiscoveryURL + IsUnifiedHost checks inline.

Follow-up to #4929 as suggested in review comment #2 (logic duplication).

Test plan

• TestResolveConfigType — 9-case table-driven unit test in libs/auth/config_type_test.go.
• All existing TestProfileLoad* and TestToOAuthArgument* tests pass.
• go test ./libs/auth/ ./cmd/auth/ passes.

[github-actions]

Approval status: pending

/cmd/auth/ - needs approval

Files: cmd/auth/profiles.go
Suggested: @simonfaltum
Also eligible: @tanmay-db, @renaudhartert-db, @tejaskochar-db, @hectorcast-db, @parthban-db, @Divyansh-db, @chrisst, @rauchy

/libs/auth/ - needs approval

Files: libs/auth/arguments.go, libs/auth/config_type.go, libs/auth/config_type_test.go
Suggested: @simonfaltum
Also eligible: @tanmay-db, @renaudhartert-db, @tejaskochar-db, @hectorcast-db, @parthban-db, @Divyansh-db, @chrisst, @rauchy

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db) can approve all areas.
See OWNERS for ownership rules.}