feat(gateway): add .ts/.py/.sh to SUPPORTED_DOCUMENT_TYPES

The gateway already accepts plain-text config files (.ini, .cfg) and
structured formats (.json, .yaml, .toml) as documents, but not common
source-file extensions. Sending a .ts/.py/.sh file currently requires
renaming it to .txt first.

Adds .ts, .py, .sh as text/plain, consistent with the existing
.ini/.cfg entries.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

gateway/platforms/base.py

@@ -829,6 +829,9 @@ SUPPORTED_DOCUMENT_TYPES = {
     ".docx": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
     ".xlsx": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
     ".pptx": "application/vnd.openxmlformats-officedocument.presentationml.presentation",
+    ".ts": "text/plain",
+    ".py": "text/plain",
+    ".sh": "text/plain",
 }