Replace shell-quote with shlex for proper $'...' ANSI-C quoting support

shell-quote doesn't support $'...' (ANSI-C quoting), which is a bash
extension used by browsers when copying requests as cURL. It misinterprets
the $ as variable expansion, mangling JSON bodies and escape sequences
like \n, \uXXXX, \r, etc.

Switches to shlex which handles $'...' natively. Adds splitCommands()
to handle command separation (;, newlines) that shell-quote used to do,
and a tokenize() wrapper with fallback for malformed input.

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

plugins/importer-curl/package.json

@@ -10,9 +10,6 @@
     "test": "vitest --run tests"
   },
   "dependencies": {
-    "shell-quote": "^1.8.1"
-  },
-  "devDependencies": {
-    "@types/shell-quote": "^1.7.5"
+    "shlex": "^3.0.0"
   }
 }