fix: correct Biome formatting and restore non-null assertions in tests

- Remove root biome.json (conflicted with packages/config/biome.json)
- Format all files with correct config (spaces, not tabs)
- Restore non-null assertions (ref!) in test files where refs are guaranteed
- Biome's optional chaining conversion broke TypeScript inference in tests

Fixes type-check and format-check CI failures.

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

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

biome.json

@@ -1,29 +0,0 @@
-{
-	"$schema": "https://biomejs.dev/schemas/1.9.4/schema.json",
-	"vcs": {
-		"enabled": true,
-		"clientKind": "git",
-		"useIgnoreFile": true
-	},
-	"files": {
-		"ignoreUnknown": false,
-		"ignore": [".next", "dist", ".turbo", "node_modules", "storybook-static"]
-	},
-	"formatter": {
-		"enabled": true,
-		"formatWithErrors": false,
-		"indentStyle": "tab",
-		"indentWidth": 2,
-		"lineWidth": 100,
-		"lineEnding": "lf"
-	},
-	"linter": {
-		"enabled": true,
-		"rules": {
-			"recommended": true,
-			"suspicious": {
-				"noExplicitAny": "warn"
-			}
-		}
-	}
-}