overhauled API:

- wrote openapi schema
- re-implemented api endpoint following openapi schema
- intensified and improved working with Result objects

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

de.srsoftware.cal.base/build.gradle.kts

@@ -4,7 +4,7 @@ dependencies {
     implementation(project(":de.srsoftware.cal.api"))
 
     implementation("de.srsoftware:tools.optionals:1.0.0")
-    implementation("de.srsoftware:tools.util:1.2.3")
+    implementation("de.srsoftware:tools.util:1.3.0")
     implementation("de.srsoftware:tools.web:1.3.8")
     implementation("org.json:json:20240303")
 }