WP-02: contracts and failing tests for settings, mail, jobs and scheduler

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/Cargo.lock

@@ -63,8 +63,10 @@ dependencies = [
  "async-trait",
  "base64",
  "chrono",
+ "cron",
  "domain",
  "rand",
+ "serde_json",
  "sha2",
  "tokio",
  "uuid",
@@ -301,6 +303,17 @@ version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "217698eaf96b4a3f0bc4f3662aaa55bdf913cd54d7204591faa790070c6d0853"
 
+[[package]]
+name = "cron"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5877d3fbf742507b66bc2a1945106bd30dd8504019d596901ddd012a4dd01740"
+dependencies = [
+ "chrono",
+ "once_cell",
+ "winnow",
+]
+
 [[package]]
 name = "crossbeam-queue"
 version = "0.3.13"
@@ -2466,6 +2479,15 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
 
+[[package]]
+name = "winnow"
+version = "0.6.26"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e90edd2ac1aa278a5c4599b1d89cf03074b610800f866d4026dc199d7929a28"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "writeable"
 version = "0.6.4"