fix: revert incorrect thn to then MIME type change

Reverts typos CLI change that incorrectly changed "thn" (Thompson/Compuserve
thumbnail format) to "then" in MIME type mappings. Adds "thn" to typos
config to prevent this false positive in the future.

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

Co-Authored-By: Claude <[email protected]>

Author: riderx

.typos.toml

@@ -41,3 +41,4 @@ extend-exclude = [
 [default.extend-words]
 # Add any custom words that should not be corrected
 # Format: incorrectword = "incorrectword"
+thn = "thn"

ios/Capacitor/Capacitor/WebViewAssetHandler.swift

@@ -450,7 +450,7 @@ open class WebViewAssetHandler: NSObject, WKURLSchemeHandler {
         "texinfo": "application/x-texinfo",
         "tgz": "application/x-compressed",
         "thmx": "application/vnd.ms-officetheme",
-        "then": "application/octet-stream",
+        "thn": "application/octet-stream",
         "tif": "image/tiff",
         "tiff": "image/tiff",
         "toc": "application/octet-stream",