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/tests/test_worktree_separate_dbs.py

@@ -295,7 +295,7 @@ async def test_mcp_works_with_separate_databases(git_worktree_with_separate_dbs,
     # Create MCP client
     async with Client(mcp) as client:
         # Set context to worktree
-        await client.call_tool("set_context", {"workspace_root": str(worktree)})
+        await client.call_tool("context", {"workspace_root": str(worktree)})
         
         # Create issue via MCP
         result = await client.call_tool(