Add missing changes from feature branch

- Update Makefile to run lint and vet before tests
- Add install target to Makefile
- Fix keychainunlocker_stub.go for non-Darwin platforms

Makefile

@@ -12,7 +12,7 @@ build: ./secret
 vet:
 	go vet ./...
 
-test:
+test: lint vet
 	go test ./... || go test -v ./...
 
 fmt:
@@ -21,9 +21,6 @@ fmt:
 lint:
 	golangci-lint run --timeout 5m
 
-# Check all code quality (build + vet + lint + unit tests)
-check: ./secret vet lint test
-
 # Build Docker container
 docker: 
 	docker build -t sneak/secret .
@@ -35,3 +32,6 @@ docker-run:
 # Clean build artifacts
 clean:
 	rm -f ./secret
+
+install: ./secret
+	cp ./secret $(HOME)/bin/secret

internal/secret/keychainunlocker_stub.go

@@ -4,9 +4,8 @@
 package secret
 
 import (
-	"fmt"
-
 	"filippo.io/age"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 )
 
@@ -67,3 +66,8 @@ func NewKeychainUnlocker(fs afero.Fs, directory string, metadata UnlockerMetadat
 func CreateKeychainUnlocker(fs afero.Fs, stateDir string) (*KeychainUnlocker, error) {
 	panic("keychain unlockers are only supported on macOS")
 }
+
+// getLongTermPrivateKey panics on non-Darwin platforms
+func getLongTermPrivateKey(fs afero.Fs, vault VaultInterface) (*memguard.LockedBuffer, error) {
+	panic("keychain unlockers are only supported on macOS")
+}