Change NewCLIInstance() and NewCLIInstanceWithFs() to return
(*Instance, error) instead of panicking on DetermineStateDir failure.
Callers in RunE contexts propagate the error. Callers in command
construction (for shell completion) use log.Fatalf. Test callers
use t.Fatalf.
Addresses review feedback on PR #18.
When os.UserConfigDir() fails, DetermineStateDir falls back to
os.UserHomeDir(). Previously the error from UserHomeDir was discarded,
which could result in a dangerous root-relative path (/.config/...) if
both calls fail.
Now DetermineStateDir returns (string, error) and propagates failures
from both UserConfigDir and UserHomeDir.
Closes#14
Fixed the first five errcheck linter errors:
- Added error handling for os.Unsetenv in cli_test.go
- Added error handling for file.Close() in crypto.go (4 instances)
Replace all os.Setenv calls with t.Setenv in test functions to ensure
proper test environment cleanup and better test isolation. This leaves
only legitimate application code and helper functions using os.Setenv.
