fix(login): remove unconditional logging of OAuth2 access and refresh tokens

[Harishrs2006]

Summary
Removes two log.Printf calls in cmd/login.go that unconditionally printed the OAuth2 access token and refresh token to stderr on every SSO login — regardless of whether --verbose was set.

Problem

// Before — leaks credentials to stderr unconditionally
log.Printf("Token: %s\n", tokenString)
log.Printf("Refresh Token: %s\n", refreshToken)

Any CI/CD pipeline or log aggregation system capturing stderr silently records long-lived credentials in plaintext. Refresh tokens are especially dangerous — they allow obtaining new access tokens without user interaction.

All other sensitive output in this codebase is gated behind config.Verbose / config.DumpRequestIfRequired. These two lines were the only exception — leftover debug statements.

Changes:
cmd/login.go: removed 2 lines — the unconditional token log statements
The fmt.Printf("Authentication successful\n") immediately above already confirms success without exposing any credential
Testing
go build ./... # clean
go test ./... # all pass
go vet ./... # clean
Manual: SSO login flow no longer prints token values to stderr. Behavior otherwise unchanged.

Fixes : #345