refactor: extract autoFormat utils from ChatMessage to lib with tests

- Move guessLanguage, looksLikeCode, autoFormatText to src/lib/autoFormat.ts
- Add comprehensive test suite (23 tests) covering language detection, code detection, and auto-formatting
- Reduce ChatMessage.tsx by ~90 lines
- Total tests: 238 (up from 215)

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "pinchchat",
-  "version": "1.68.2",
+  "version": "1.68.3",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "pinchchat",
-      "version": "1.68.2",
+      "version": "1.68.3",
       "license": "MIT",
       "dependencies": {
         "@tailwindcss/vite": "^4.1.18",