Implement terrain symbol generation profiles

README.md

@@ -96,7 +96,8 @@ Panel, it describes a randomly generated Age. Authored writing is compiled once
 into a versioned, server-owned Age plan. The plan freezes the Age seed, resolved
 symbol meanings, page order, and runtime profile, so later data-pack changes do
 not reinterpret an existing Age. An authored terrain page selects its runtime
-profile; other symbol effects are scheduled for later Milestone 5 slices. The
+profile. Built-in pages cover Standard, Amplified, Cave, Island, Flat, and Void;
+other symbol effects are scheduled for later Milestone 5 slices. The
 writing is also stored on the book; the Descriptive Book screen's turned pages
 show ordered symbols and unresolved IDs. The Descriptive Book screen follows
 Legacy's book spread: the title and Age details are on the left, the destination