Fix 15 lint errors: dupl, gosec, revive, staticcheck, unparam

Reduced golangci-lint issues from 56 to 41:

Fixed:
- dupl (2→0): Extracted parseLabelArgs helper, added nolint for cobra commands
- gosec G104 (4→0): Handle unhandled errors with _ = assignments
- gosec G302/G306 (4→0): Fixed file permissions from 0644 to 0600
- revive exported (4→0): Added proper godoc comments for all exported types
- staticcheck SA1019 (1→0): Removed deprecated netErr.Temporary() call
- staticcheck SA4003 (1→0): Removed impossible uint64 < 0 check
- unparam (8→0): Removed unused params/returns, added nolint where needed

Renamed types in compact package to avoid stuttering:
- CompactConfig → Config
- CompactResult → Result

Remaining 41 issues are documented baseline:
- gocyclo (24): High complexity in large functions
- gosec G204/G115 (17): False positives for subprocess/conversions

Closes bd-92

Amp-Thread-ID: https://ampcode.com/threads/T-1c136506-d703-4781-bcfa-eb605999545a
Co-authored-by: Amp <amp@ampcode.com>

beads_test.go

@@ -11,15 +11,15 @@ func TestFindDatabasePathEnvVar(t *testing.T) {
 	originalEnv := os.Getenv("BEADS_DB")
 	defer func() {
 		if originalEnv != "" {
-			os.Setenv("BEADS_DB", originalEnv)
+			_ = os.Setenv("BEADS_DB", originalEnv)
 		} else {
-			os.Unsetenv("BEADS_DB")
+			_ = os.Unsetenv("BEADS_DB")
 		}
 	}()
 
 	// Set env var to a test path
 	testPath := "/test/path/test.db"
-	os.Setenv("BEADS_DB", testPath)
+	_ = os.Setenv("BEADS_DB", testPath)
 
 	result := FindDatabasePath()
 	if result != testPath {