PB: database_test.go doesn't isolate DB_* env vars, so tests can fail depending on process environment

[mushrafmim]

Describe the Bug

internal/pb/v1/database_test.go:

• TestNewDatabaseConfig (lines ~11-23) asserts default values ("localhost", "5432", etc.) without clearing any DB_* env vars first, so it fails if the test process already has one set.
• TestNewDatabaseConfig_WithEnvVars (lines ~26-49) sets DB_* vars with manual os.Setenv and manually os.Unsetenvs them in t.Cleanup, rather than restoring whatever value (if any) existed beforehand.

Surfaced by CodeRabbit reviewing #517 — this code predates that PR, it just moved location (was portal-backend/v1/database_test.go).

Expected Behavior

Use t.Setenv for every DB_* variable in both tests — set explicit empty values in TestNewDatabaseConfig before asserting defaults, and use t.Setenv (instead of manual os.Setenv/os.Unsetenv) in TestNewDatabaseConfig_WithEnvVars, since t.Setenv automatically restores the prior value after the test and fails the test if run with t.Parallel() misuse.

Version

Surfaced on PR #517 (refactor/portal-backend-restructure).

Additional Context

Flagged 🟡 Minor (Functional Correctness) by CodeRabbit.