Add SSO login support

- Add [sso] config section with redirect_uri
- Create mcdsl/sso client when SSO is configured
- Add /login (landing page), /sso/redirect, /sso/callback routes
- Add /logout route
- Update login template with SSO landing page variant
- Bump mcdsl to v1.6.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/git.wntrmute.dev/kyle/goutils/lib/defs.go

@@ -0,0 +1,21 @@
+package lib
+
+// Various constants used throughout the tools.
+
+const (
+	// ExitSuccess is the successful exit status.
+	//
+	// It should be called on successful exit.
+	ExitSuccess = 0
+
+	// ExitFailure is the failing exit status.
+	ExitFailure = 1
+)
+
+const (
+	OneTrueDateFormat    = "2006-01-02T15:04:05-0700"
+	DateShortFormat      = "2006-01-02"
+	TimeShortFormat      = "15:04:05"
+	TimeShorterFormat    = "15:04"
+	TimeStandardDateTime = "2006-01-02 15:04"
+)