fix: Remove unsupported env vars and fix slash commands directory structure

Fixes #42 and #44

- Remove BEADS_ACTOR and BEADS_WORKING_DIR from plugin.json env
  (Claude Code only supports ${CLAUDE_PLUGIN_ROOT} expansion)
- Move commands from .claude-plugin/commands/ to commands/ at root
- Rename command files to remove redundant bd- prefix

This fixes MCP server crashes with literal ${PWD} directory errors
and makes slash commands discoverable in Claude Code.

Amp-Thread-ID: https://ampcode.com/threads/T-69426d6c-25ea-4333-8955-5b624001c8c6
Co-authored-by: Amp <amp@ampcode.com>

commands/version.md

@@ -0,0 +1,26 @@
+---
+description: Check beads and plugin versions
+---
+
+Check the installed versions of beads components and verify compatibility.
+
+**Note:** The MCP server automatically checks bd CLI version >= 0.9.0 on startup. This command provides detailed version info and update instructions.
+
+Use the beads MCP tools to:
+1. Run `bd version` via bash to get the CLI version
+2. Check the plugin version (0.9.2)
+3. Compare versions and report any mismatches
+
+Display:
+- bd CLI version (from `bd version`)
+- Plugin version (0.9.2)
+- MCP server version (0.9.2)
+- MCP server status (from `stats` tool or connection test)
+- Compatibility status (✓ compatible or ⚠️ update needed)
+
+If versions are mismatched, provide instructions:
+- Update bd CLI: `curl -fsSL https://raw.githubusercontent.com/steveyegge/beads/main/install.sh | bash`
+- Update plugin: `/plugin update beads`
+- Restart Claude Code after updating
+
+Suggest checking for updates if the user is on an older version.