fix: quote CLAUDE_PLUGIN_ROOT for spaces, use POSIX-safe path resolution

- Quote ${CLAUDE_PLUGIN_ROOT} in hooks.json to handle paths with spaces
  (e.g. "C:\Users\Robert Zimmermann\...")
- Replace bash-only ${BASH_SOURCE[0]:-$0} with POSIX-safe $0 in
  run-hook.cmd so the Unix path doesn't break on dash (/bin/sh)

Addresses: #518 (spaces in path), Ubuntu/Debian compatibility

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

hooks/hooks.json

@@ -6,7 +6,7 @@
         "hooks": [
           {
             "type": "command",
-            "command": "${CLAUDE_PLUGIN_ROOT}/hooks/run-hook.cmd session-start",
+            "command": "'${CLAUDE_PLUGIN_ROOT}/hooks/run-hook.cmd' session-start",
             "async": false
           }
         ]