feat: make invite link base URL configurable via APP_URL

Load environment variables from .env file using godotenv.
Defaults to https://demo.adriatica.io if APP_URL is not set.

go.mod

@@ -4,10 +4,10 @@ go 1.25.4
 
 require (
 	github.com/google/uuid v1.6.0
+	github.com/joho/godotenv v1.5.1
 	github.com/pressly/goose/v3 v3.26.0
 	github.com/ryanhamamura/via v0.4.0
 	golang.org/x/crypto v0.47.0
-	maragu.dev/gomponents v1.2.0
 	modernc.org/sqlite v1.44.0
 )
 
@@ -43,6 +43,7 @@ require (
 	golang.org/x/sync v0.18.0 // indirect
 	golang.org/x/sys v0.40.0 // indirect
 	golang.org/x/time v0.14.0 // indirect
+	maragu.dev/gomponents v1.2.0 // indirect
 	modernc.org/libc v1.67.4 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect