feat: optional property rent

Off unless property_rent_enabled is on. Each property world's rent comes from its PropertyTemplate
row (minimumPrice every rentDuration x durationType; Block Yard is free), unless the new Property
Rent dashboard page sets another price or period (property_rent_manage). Rent is taken from the
owner's coins shortly after their character loads, with a mail receipt; unpaid rent is mailed and,
after property_rent_grace_days, makes the property private until it is paid, like live. The
property management component refuses public or best friends privacy while rent is overdue and a
property world that loads overdue makes itself private. Property game messages are unchanged.

Fixes #943

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

migrations/dlu/mysql/78_property_rent.sql

@@ -0,0 +1,9 @@
+/* Property rent: a price (coins, 0: free) and period (days, 0: the template's) per property world set on the
+   dashboard, overriding PropertyTemplate's. properties.rent_due (unused until now) is when the next rent is due. */
+CREATE TABLE IF NOT EXISTS property_rent_rates (
+    map_id INT NOT NULL PRIMARY KEY,
+    price BIGINT NOT NULL DEFAULT 0,
+    period_days INT NOT NULL DEFAULT 0,
+    updated_by VARCHAR(64) NOT NULL DEFAULT '',
+    updated_at BIGINT NOT NULL DEFAULT 0
+);

migrations/dlu/sqlite/61_property_rent.sql

@@ -0,0 +1,8 @@
+/* property_rent_rates: see the MySQL migration. */
+CREATE TABLE IF NOT EXISTS property_rent_rates (
+	map_id INTEGER NOT NULL PRIMARY KEY,
+	price BIGINT NOT NULL DEFAULT 0,
+	period_days INTEGER NOT NULL DEFAULT 0,
+	updated_by TEXT NOT NULL DEFAULT '',
+	updated_at BIGINT NOT NULL DEFAULT 0
+);