fix(mcp): Run bd commands in user's working directory

The MCP server was running bd commands from the plugin installation directory,
causing the database to be created in the wrong place.

Added BEADS_WORKING_DIR config option and modified BdClient to use working
directory for subprocess calls. Falls back to PWD environment variable.

This ensures bd commands run from the user's actual project directory.

🤖 Generated with Claude Code

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

integrations/beads-mcp/src/beads_mcp/config.py

@@ -36,6 +36,7 @@ class Config(BaseSettings):
     beads_actor: str | None = None
     beads_no_auto_flush: bool = False
     beads_no_auto_import: bool = False
+    beads_working_dir: str | None = None
 
     @field_validator("beads_path")
     @classmethod
@@ -132,6 +133,7 @@ def load_config() -> Config:
             + "Advanced configuration (optional):\n"
             + f"  BEADS_PATH            - Path to bd executable (default: {default_path})\n"
             + "  BEADS_DB              - Path to beads database file (default: auto-discover)\n"
+            + "  BEADS_WORKING_DIR     - Working directory for bd commands (default: $PWD or cwd)\n"
             + "  BEADS_ACTOR           - Actor name for audit trail (default: $USER)\n"
             + "  BEADS_NO_AUTO_FLUSH   - Disable automatic JSONL sync (default: false)\n"
             + "  BEADS_NO_AUTO_IMPORT  - Disable automatic JSONL import (default: false)"