feat(drivers/139): optimize login credential flow

[UcnacDx2]

Summary

• add 139Yun login initialization with Authorization, mail cookie fast login, and password fallback paths
• reject Authorization values that include the Basic prefix
• add opt-in live login coverage driven by environment variables, without storing credentials in tests

Tests

• go test ./drivers/139
• go test -vet=off ./drivers/139 ./pkg/cookie
• Live 139Yun login test with local env vars: password fallback passed, generated Authorization passed, refreshed cookie fast login passed; direct input cookie fast login skipped when RMKEY was absent

Notes

• Live tests are skipped by default and require ALIST_139_INTEGRATION=1 plus local credentials/cookies.

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