fix: address review informational issues + add regression tests

- Add cookie-import to CHAIN_WRITE set for chain command routing
- Add path validation to snapshot -a -o output path
- Fix package.json version to match 0.3.1
- Use crypto.randomUUID() for temp DB paths (unpredictable filenames)
- Add regression tests for chain cookie-import and snapshot path validation

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gstack",
-  "version": "0.0.1",
+  "version": "0.3.1",
   "description": "Garry's Stack — Claude Code skills + fast headless browser. One repo, one install, entire AI engineering workflow.",
   "license": "MIT",
   "type": "module",