Downgrade styled-components to v5 for TypeScript compatibility

- Downgrade styled-components from v6.1.1 to v5.3.11
- Add @types/styled-components for v5 type definitions
- Simplify styled.ts export (v5 uses default export)
- Remove tsconfig skipLibCheck workaround (not needed with v5)
- Add string-replace-loader dependency for webpack
- Update @pezkuwi/dev to 0.85.4 (includes rollup config export fix)

This fixes TS2742 declaration emit errors that prevented npm
package builds while allowing Chrome/Firefox extension bundles.

packages/extension/package.json

@@ -38,6 +38,7 @@
     "path-browserify": "^1.0.1",
     "process": "^0.11.10",
     "stream-browserify": "^3.0.0",
+    "string-replace-loader": "^3.1.0",
     "ts-loader": "^9.5.1",
     "url-loader": "^4.1.1",
     "webpack-extension-manifest-plugin": "^0.8.0"