release: v0.7.13 — Developer-ID signed + notarized macOS

- bump version 0.7.12 -> 0.7.13 across package.json, Cargo.toml,
  tauri.conf.json, website version string, and version tests
- README: update both download tables + tag instructions to v0.7.13,
  add v0.7.13 changelog entry
- website: remove the sudo xattr quarantine hint (macOS is now signed +
  notarized), drop the copy-quarantine handler + macos-hint animation
  from landing.js, add v0.7.13 changelog entry

desktop/src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Gridline",
-  "version": "0.7.12",
+  "version": "0.7.13",
   "identifier": "com.adrianbonpin.gridline",
   "build": {
     "beforeDevCommand": "bun run dev",