Add workflow permission hook

[hccnm]

Summary

• Adds first-class Workflow tool display/result parsing and session-level workflow run tracking.
• Routes Workflow tool launches through the existing ACP requestPermission surface with run_once, view_script, and deny options.
• Applies the same permission hook to workflow slash command dispatch before the prompt is sent to the SDK, with a single-turn grant to avoid duplicate approval when the SDK invokes the matching Workflow tool.
• Exposes workflow state through _claude/workflows/list, _claude/workflows/get, _claude/workflows/stop, and workflow update notifications.

Notes

• ACP does not make business approval decisions. It only exposes the workflow launch interception point and relays the client choice.
• /workflows remains local-only and does not enter the model.
• bypassPermissions continues to allow Workflow tool use without prompting.

Validation

• npm ci
• npm run format:check
• npm run lint
• npm run build
• npm run test:run