Implement production-ready block designer and schema

- Add EnhancedBlockDesigner with Scratch-like block interface - Remove
all legacy designer implementations (React Flow, FreeForm, etc.) - Add
block registry and plugin schema to database - Update experiments table
with visual_design, execution_graph, plugin_dependencies columns and GIN
index - Update drizzle config to use hs_* table filter - Add block
shape/category enums to schema - Update experiment designer route to use
EnhancedBlockDesigner - Add comprehensive documentation for block
designer and implementation tracking

drizzle.config.ts

@@ -8,5 +8,5 @@ export default {
   dbCredentials: {
     url: env.DATABASE_URL,
   },
-  tablesFilter: ["hristudio_*"],
+  tablesFilter: ["hs_*"],
 } satisfies Config;