Registration: replace date-of-birth field with a simple 18+ confirmation

The register form collected and validated an actual date of birth just to
throw it away (backend never stored it beyond a nullable column). Per the
roadmap note: don't collect/store DOB right now, just get a client-side
"I am 18 or older" confirmation. RegisterRequest.date_of_birth (str) is now
over_18 (bool); the endpoint rejects over_18=false with 400 same as before.
calculate_age() is kept (unused by /register now) since real DOB collection
is coming back in a future pass and deleting it broke test_auth_age_gate.py's
import for no benefit.

Frontend: DOBEdit LineEdit replaced with an Over18Check CheckBox; api_client.gd's
register() now takes a bool instead of a date string. All Godot callers
(smoke_test_auth/e2e/world_list/main_menu_ui/main_menu_full_flow) and backend
test files updated to match. Full suite verified against a live backend:
61/61 pytest, 6/6 Godot smoke tests (33 individual assertions), all passing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M6rUEynmv2QmweocAQYARN

backend/tests/test_auth_endpoints.py

@@ -73,7 +73,7 @@ class TestRegister:
                 "username": "newuser",
                 "email": "new@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "over_18": True,
             },
         )
         assert resp.status_code == 201
@@ -81,8 +81,14 @@ class TestRegister:
         assert "access_token" in data
         assert data["token_type"] == "bearer"
 
-    def test_register_rejects_underage(self):
-        """Users under 18 get a 400 with a detail message."""
+    def test_register_rejects_not_over_18(self):
+        """over_18=false gets a 400 with a detail message.
+
+        The interim design (2026-08-20) trusts a client-side boolean
+        confirmation instead of collecting/validating an actual date of
+        birth -- this only checks that the flag is respected, not real
+        age math (there's no date to verify against anymore). Real DOB
+        collection/verification may come back in a future pass."""
         client = TestClient(app)
         resp = client.post(
             "/api/auth/register",
@@ -90,7 +96,7 @@ class TestRegister:
                 "username": "kid",
                 "email": "kid@example.com",
                 "password": "secret123",
-                "date_of_birth": "2010-06-15",  # ~15 years old
+                "over_18": False,
             },
         )
         assert resp.status_code == 400
@@ -106,7 +112,7 @@ class TestRegister:
                 "username": "duplicate",
                 "email": "dup1@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "over_18": True,
             },
         )
         # Second registration with same username, different email
@@ -116,7 +122,7 @@ class TestRegister:
                 "username": "duplicate",
                 "email": "dup2@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "over_18": True,
             },
         )
         assert resp.status_code == 409
@@ -131,7 +137,7 @@ class TestRegister:
                 "username": "user1",
                 "email": "same@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "over_18": True,
             },
         )
         resp = client.post(
@@ -140,14 +146,19 @@ class TestRegister:
                 "username": "user2",
                 "email": "same@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "over_18": True,
             },
         )
         assert resp.status_code == 409
         assert "Email already registered" in resp.json()["detail"]
 
-    def test_register_invalid_date_format(self):
-        """Invalid date format returns 422 validation error."""
+    def test_register_missing_over_18(self):
+        """Missing the required over_18 field returns 422.
+
+        Replaces the old test_register_invalid_date_format -- there's no
+        date format to get wrong anymore (no date field at all), so the
+        closest equivalent "malformed request" case is the required
+        over_18 boolean being absent entirely."""
         client = TestClient(app)
         resp = client.post(
             "/api/auth/register",
@@ -155,25 +166,10 @@ class TestRegister:
                 "username": "user",
                 "email": "user@example.com",
                 "password": "secret123",
-                "date_of_birth": "01-01-2000",  # wrong format
             },
         )
         assert resp.status_code == 422
 
-    def test_register_exactly_18(self):
-        """A user who just turned 18 can register."""
-        client = TestClient(app)
-        resp = client.post(
-            "/api/auth/register",
-            json={
-                "username": "just18",
-                "email": "just18@example.com",
-                "password": "secret123",
-                "date_of_birth": "2007-06-15",
-            },
-        )
-        assert resp.status_code == 201
-
 
 # ---------------------------------------------------------------------------
 # Login endpoint
@@ -193,7 +189,7 @@ class TestLogin:
                 "username": username,
                 "email": email,
                 "password": password,
-                "date_of_birth": "2000-01-01",
+                "over_18": True,
             },
         )
         assert resp.status_code == 201