Audit Legacy instability and allow unstable supported writing

Persist repaired Age writing and provisional instability penalties, retain fatal diagnostics for unsupported content, and hide TerraBlender's deferred placeholder biome from creative and JEI.

src/main/resources/assets/rivencraft/lang/en_us.json

@@ -47,10 +47,10 @@
   "screen.rivencraft.book_binder.grammar.unsupported": "Page %s: this symbol needs semantic schema v2; update its data pack or remove it",
   "screen.rivencraft.book_binder.grammar.unsupported_profile": "Page %s: its Age profile is unavailable; restore the data pack or remove this page",
   "screen.rivencraft.book_binder.grammar.unsupported_environment": "Page %s: this weather or sky effect is not supported yet",
-  "screen.rivencraft.book_binder.grammar.duplicate": "Page %s: remove the duplicate symbol",
-  "screen.rivencraft.book_binder.grammar.conflict": "Page %s: replace the conflicting symbol",
-  "screen.rivencraft.book_binder.grammar.out_of_order": "Page %s: move this symbol before later categories",
-  "screen.rivencraft.book_binder.grammar.misplaced_modifier": "Page %s: move this modifier before its celestial page",
+  "screen.rivencraft.book_binder.grammar.duplicate": "Page %s: duplicate page adds instability; the last choice is used",
+  "screen.rivencraft.book_binder.grammar.conflict": "Page %s: conflicting page adds instability; the supported choice is used",
+  "screen.rivencraft.book_binder.grammar.out_of_order": "Page %s: incorrect order adds instability; the Age repairs the order",
+  "screen.rivencraft.book_binder.grammar.misplaced_modifier": "Page %s: misplaced modifier adds instability; the Age repairs its order",
   "screen.rivencraft.writing_desk.ink": "Ink: %s/%s",
   "screen.rivencraft.writing_desk.search": "Search",
   "screen.rivencraft.writing_desk.sort": "Sort pages by name (A–Z)",