fix(cursor): run SessionStart hook via run-hook.cmd on Windows

Route Cursor's Windows SessionStart hook through the existing run-hook.cmd dispatcher instead of invoking the extensionless session-start script directly. This avoids Windows opening the extensionless hook file and lets Git Bash run the script as intended.

Also removed an accidental UTF-8 BOM from hooks-cursor.json before merging.

Verified:
- hooks-cursor.json parses as JSON and has no BOM
- command is ./hooks/run-hook.cmd session-start
- CURSOR_PLUGIN_ROOT=/tmp/superpowers ./hooks/run-hook.cmd session-start emits valid Cursor JSON with additional_context

hooks/hooks-cursor.json

@@ -3,7 +3,7 @@
   "hooks": {
     "sessionStart": [
       {
-        "command": "./hooks/session-start"
+        "command": "./hooks/run-hook.cmd session-start"
       }
     ]
   }