fix: Worktree scripts use $(pwd) for project root

Scripts now correctly determine project root from current working
directory instead of calculating relative to script location.
This fixes the issue when scripts are called via ${CLAUDE_PLUGIN_ROOT}.

Also adds CLAUDE.md and CHANGELOG.md for development guidance.

Bumps version to 1.0.3.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "ab",
   "description": "Auto-Build: Spec-driven build orchestration with worktree isolation and session memory",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "author": {
     "name": "ROA2WEB Team"
   }