chore: remove strands agent workflows and action

Remove the strands-command, agent-restricted workflows, the
strands-action composite action, and all supporting scripts.
These are maintained in the private staging repo instead.

Removes:
- .github/workflows/strands-command.yml
- .github/workflows/agent-restricted.yml
- .github/actions/strands-action/
- .github/scripts/ (agent_runner, github_tools, process-inputs, etc.)

Author: aidandaly24