feat: go 1.25.5, dependency updates, renamed internal/errors (#129)

* feat: rename internal/errors to internal/apperrors

* fix(tests): clear env values before using in tests

* feat: rename internal/errors to internal/apperrors

* chore(deps): update go and all dependencies

* chore: remove renovate from pre-commit, formatting

* chore: sonarcloud fixes

* feat: consolidate constants to appconstants/constants.go

* chore: sonarcloud fixes

* feat: simplification, deduplication, test utils

* chore: sonarcloud fixes

* chore: sonarcloud fixes

* chore: sonarcloud fixes

* chore: sonarcloud fixes

* chore: clean up

* fix: config discovery, const deduplication

* chore: fixes

internal/github_helper.go

@@ -0,0 +1,25 @@
+package internal
+
+import (
+	"os"
+
+	"github.com/ivuorinen/gh-action-readme/appconstants"
+)
+
+// loadGitHubTokenFromEnv retrieves the GitHub token from environment variables.
+// It checks both the tool-specific environment variable (GHREADME_GITHUB_TOKEN)
+// and the standard GitHub environment variable (GITHUB_TOKEN) in that order.
+// Returns an empty string if no token is found.
+func loadGitHubTokenFromEnv() string {
+	// Priority 1: Tool-specific env var
+	if token := os.Getenv(appconstants.EnvGitHubToken); token != "" {
+		return token
+	}
+
+	// Priority 2: Standard GitHub env var
+	if token := os.Getenv(appconstants.EnvGitHubTokenStandard); token != "" {
+		return token
+	}
+
+	return ""
+}