0.37.5: overwrite prompt for file upload + auto-reveal uploaded hidden files

The reported "upload doesn't work, file never appears" was two things, both
hit when uploading config files like .env:

1. Single-file upload used overwrite=false and dead-ended on "Already
   exists: .env — rename or remove the existing file first." with no way to
   replace the file. Now a conflict opens an Overwrite confirmation dialog
   (mirroring the copy/paste conflict flow) that retries with overwrite=true.
2. .env (and any dotfile) is hidden, so even a successful upload stayed
   invisible unless "Show hidden" was on. After an upload whose name/path
   has a dot-segment, "Show hidden" is now auto-enabled so the file shows.

The single-file upload mutation now takes {file, overwrite}; folder upload
(already overwrite=true) also auto-reveals hidden results.

Frontend-only; all 3 images rebuilt+pushed 0.37.5.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "stackpilot-frontend",
   "private": true,
-  "version": "0.37.4",
+  "version": "0.37.5",
   "type": "module",
   "scripts": {
     "dev": "vite",