feat(db): add feature flags schema for beta feature testing

Add feature_flags and feature_flag_access tables to support controlled
beta testing of new features in production without a separate test environment.

shared/db/migrations/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1767716705797,
       "tag": "0002_fancy_forge",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "7",
+      "when": 1770903573324,
+      "tag": "0003_new_senator_kelly",
+      "breakpoints": true
     }
   ]
 }