Enable noInnerDeclarations lint rule

The var to let/const modernisation resolved all noInnerDeclarations violations
by moving variable declarations to proper block scope with let/const.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: cressie176

biome.json

@@ -22,7 +22,7 @@
       "correctness": {
         "noUnusedFunctionParameters": "error",
         "noUnusedVariables": "error",
-        "noInnerDeclarations": "off",
+        "noInnerDeclarations": "error",
         "useParseIntRadix": "off",
         "noSwitchDeclarations": "off",
         "noInvalidUseBeforeDeclaration": "off",