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>

.claude-plugin/marketplace.json

@@ -11,7 +11,7 @@
       "name": "ab",
       "source": "./plugin",
       "description": "Spec-driven build orchestration with git worktree isolation and session memory",
-      "version": "1.0.2",
+      "version": "1.0.3",
       "keywords": ["build", "spec", "automation", "worktree", "qa"]
     }
   ]