Replace ESLint with Biome for linting.

Removes ESLint 5.x with Airbnb style guide and adds Biome with
recommended rules. Formatter is disabled; JSON linting is disabled.
ESLint config files are deleted. Code fixes for Biome rule violations
will follow in a separate commit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: gaurav

.eslintrc.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://biomejs.dev/schemas/1.9.4/schema.json",
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "recommended": true
+    }
+  },
+  "formatter": {
+    "enabled": false
+  },
+  "json": {
+    "linter": {
+      "enabled": false
+    }
+  }
+}