test: add Vitest coverage for EnvManager store

[nullxnothing]

The EnvManager store is missing unit tests. Add tests covering: loading env vars, masking secrets, editing values, persistence. Match the style of existing store tests in test/.

Files: test/envManager.test.ts (new)

[Synergy738]

Hi I'm a new contributer and would like to fix this issue. Let me know if it's okay to proceed.