finish phase 4: drop @atproto/api dependency, lex-only errors, delete toLex and legacy validators

oxlint-suppressions.json gains a baseline entry for webpack.config.js: the
file was never previously staged/linted (lint script covers src+modules
only), and editing it exposed its pre-existing violations to lint-staged.
All suppressed counts are pre-existing; this change only removes a line.

oxlint-suppressions.json

@@ -1813,5 +1813,16 @@
     "typescript/no-unsafe-member-access": {
       "count": 3
     }
+  },
+  "webpack.config.js": {
+    "import/no-nodejs-modules": {
+      "count": 1
+    },
+    "typescript/no-unsafe-call": {
+      "count": 11
+    },
+    "typescript/no-unsafe-member-access": {
+      "count": 30
+    }
   }
 }