feat(mcp): Consolidate context tools into unified 'context' tool

Merge set_context, where_am_i, and init into a single 'context' tool
with action parameter (set, show, init).

- set: Set the workspace root directory (default when workspace_root provided)
- show: Show current workspace context (default when no args)
- init: Initialize beads in the current workspace directory

This reduces tool count from 3 to 1 while maintaining all functionality.

Closes beads-eub

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

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

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

@@ -255,7 +255,7 @@ async def _get_client() -> BdClientBase:
     if not workspace:
         raise BdError(
             "No beads workspace found. Either:\n"
-            "  1. Call set_context(workspace_root=\"/path/to/project\"), OR\n"
+            "  1. Call context(workspace_root=\"/path/to/project\"), OR\n"
             "  2. Run from a directory containing .beads/, OR\n"
             "  3. Set BEADS_WORKING_DIR environment variable"
         )