refactor: move domain inline tests to separate files under tests/

Match the application crate convention: each source file references its
tests via #[cfg(test)] #[path = "tests/filename.rs"] mod tests; with
the test code in a sibling tests/ directory.

- events.rs       -> tests/events.rs
- value_objects.rs -> tests/value_objects.rs
- models/mod.rs   -> models/tests/mod.rs  (renamed from tests.rs)
- models/person.rs -> models/tests/person.rs
- models/goal.rs   -> models/tests/goal.rs
- models/watch_event.rs -> models/tests/watch_event.rs
- services/review_history.rs -> services/tests/review_history.rs

crates/domain/src/models/tests/goal.rs

@@ -0,0 +1,91 @@
+use super::*;
+use crate::value_objects::UserId;
+
+fn make_goal(year: u16, target: u32) -> Result<Goal, DomainError> {
+    Goal::new(UserId::generate(), year, target, GoalType::Movies)
+}
+
+#[test]
+fn new_goal_valid() {
+    let g = make_goal(2024, 52);
+    assert!(g.is_ok());
+    let g = g.unwrap();
+    assert_eq!(g.year(), 2024);
+    assert_eq!(g.target_count(), 52);
+}
+
+#[test]
+fn new_goal_rejects_year_before_2020() {
+    assert!(make_goal(2019, 10).is_err());
+}
+
+#[test]
+fn new_goal_rejects_zero_target() {
+    assert!(make_goal(2024, 0).is_err());
+}
+
+#[test]
+fn update_target_valid() {
+    let mut g = make_goal(2024, 10).unwrap();
+    assert!(g.update_target(50).is_ok());
+    assert_eq!(g.target_count(), 50);
+}
+
+#[test]
+fn update_target_rejects_zero() {
+    let mut g = make_goal(2024, 10).unwrap();
+    assert!(g.update_target(0).is_err());
+}
+
+#[test]
+fn from_persistence_preserves_fields() {
+    let id = GoalId::generate();
+    let uid = UserId::generate();
+    let ts = chrono::Utc::now().naive_utc();
+    let g = Goal::from_persistence(id.clone(), uid.clone(), 2025, 42, GoalType::Movies, ts);
+    assert_eq!(*g.id(), id);
+    assert_eq!(*g.user_id(), uid);
+    assert_eq!(g.year(), 2025);
+    assert_eq!(g.target_count(), 42);
+    assert_eq!(g.created_at(), &ts);
+}
+
+#[test]
+fn percentage_calculation() {
+    let g = make_goal(2024, 100).unwrap();
+    let wp = GoalWithProgress {
+        goal: g,
+        current_count: 50,
+    };
+    assert!((wp.percentage() - 50.0).abs() < f64::EPSILON);
+}
+
+#[test]
+fn percentage_caps_at_100() {
+    let g = make_goal(2024, 10).unwrap();
+    let wp = GoalWithProgress {
+        goal: g,
+        current_count: 20,
+    };
+    assert!((wp.percentage() - 100.0).abs() < f64::EPSILON);
+}
+
+#[test]
+fn is_complete() {
+    let g = make_goal(2024, 10).unwrap();
+    let wp = GoalWithProgress {
+        goal: g,
+        current_count: 10,
+    };
+    assert!(wp.is_complete());
+}
+
+#[test]
+fn is_not_complete() {
+    let g = make_goal(2024, 10).unwrap();
+    let wp = GoalWithProgress {
+        goal: g,
+        current_count: 9,
+    };
+    assert!(!wp.is_complete());
+}