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

scripts/main_menu.gd

@@ -17,7 +17,7 @@ var _auth_mode_label: Label
 var _username_edit: LineEdit
 var _password_edit: LineEdit
 var _email_edit: LineEdit
-var _dob_edit: LineEdit
+var _over_18_check: CheckBox
 var _auth_button: Button
 var _status_label: Label
 var _welcome_label: Label
@@ -40,7 +40,7 @@ func _ready() -> void:
 	_username_edit = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/UsernameEdit
 	_password_edit = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/PasswordEdit
 	_email_edit = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/EmailEdit
-	_dob_edit = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/DOBEdit
+	_over_18_check = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/Over18Check
 	_auth_button = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/AuthButton
 	_status_label = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/AuthStatusLabel
 	_welcome_label = $CenterContainer/VBoxContainer/AuthPanel/MarginContainer/AuthVBox/WelcomeLabel
@@ -52,7 +52,8 @@ func _ready() -> void:
 	_status_label.visible = false
 	_welcome_label.visible = false
 	_email_edit.visible = false
-	_dob_edit.visible = false
+	_over_18_check.visible = false
+	_over_18_check.button_pressed = false
 	_play_button.disabled = true  # Gate play behind successful auth.
 	_update_auth_mode_ui()
 
@@ -97,12 +98,12 @@ func _update_auth_mode_ui() -> void:
 		_auth_mode_label.text = "Register"
 		_auth_button.text = "Register"
 		_email_edit.visible = true
-		_dob_edit.visible = true
+		_over_18_check.visible = true
 	else:
 		_auth_mode_label.text = "Login"
 		_auth_button.text = "Login"
 		_email_edit.visible = false
-		_dob_edit.visible = false
+		_over_18_check.visible = false
 
 
 # ─── Auth submission ──────────────────────────────────────────────────────────
@@ -125,17 +126,12 @@ func _on_auth_button_pressed() -> void:
 
 	if _is_register_mode:
 		var email := _email_edit.text.strip_edges()
-		var dob := _dob_edit.text.strip_edges()
 
 		if email == "":
 			_show_status("Email is required.")
 			return
-		if dob == "":
-			_show_status("Date of birth is required.")
-			return
-		# Basic YYYY-MM-DD format check.
-		if not _is_valid_date(dob):
-			_show_status("Date of birth must be in YYYY-MM-DD format.")
+		if not _over_18_check.button_pressed:
+			_show_status("You must confirm you are 18 or older to register.")
 			return
 
 		_auth_button.disabled = true
@@ -143,7 +139,7 @@ func _on_auth_button_pressed() -> void:
 		_is_authenticating = true
 		_clear_status()
 
-		var result := await ApiClient.register(username, email, password, dob)
+		var result := await ApiClient.register(username, email, password, true)
 		_on_auth_complete(result)
 	else:
 		_auth_button.disabled = true
@@ -186,26 +182,3 @@ func _show_status(message: String) -> void:
 func _clear_status() -> void:
 	_status_label.text = ""
 	_status_label.visible = false
-
-
-# ─── Validation ───────────────────────────────────────────────────────────────
-
-func _is_valid_date(date_str: String) -> bool:
-	"""Check if a string looks like a valid YYYY-MM-DD date."""
-	if date_str.length() != 10:
-		return false
-	var parts := date_str.split("-")
-	if parts.size() != 3:
-		return false
-	var year := parts[0].to_int()
-	var month := parts[1].to_int()
-	var day := parts[2].to_int()
-	if month < 1 or month > 12:
-		return false
-	if day < 1 or day > 31:
-		return false
-	# Rough month-day validation.
-	var days_in_month := [0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
-	if day > days_in_month[month]:
-		return false
-	return true