Bug: MCP dispatch fallback doesn't forward user role for RBAC filtering

[mrveiss]

Problem

The _try_mcp_dispatch() function in chat_workflow/tool_handler.py (#2513) calls dispatcher.dispatch(tool_name, arguments) without passing the user's role. The RBAC filtering added in #2598 defaults role="user", so admin users can't access admin-only MCP tools (client_list, slowlog, etc.) through the chat dispatch path.

The user's role is available in the session/workflow context but isn't threaded through to the MCP dispatcher.

Fix

1. Pass user role from the session context into _try_mcp_dispatch()
2. Thread it through to dispatcher.dispatch(tool_name, arguments, role=user_role)
3. Also pass to _get_mcp_tools_prompt() in ChatAgent so admin users see admin tools in their prompt

Files Affected

• autobot-backend/chat_workflow/tool_handler.py — _try_mcp_dispatch() and _dispatch_tool_call()
• autobot-backend/agents/chat_agent.py — _get_mcp_tools_prompt() and process_chat_message()

Discovered During

Review of #2596/#2598 implementation.

Impact

Medium — RBAC filtering works but admin users are incorrectly restricted to user-level tools.

[mrveiss]

Merged via PR #2647. RBAC role now forwarded through _try_mcp_dispatch → dispatcher.dispatch(role=role). 18/18 tests passing.