Turns each DSH workspace folder into a project

Key features

• Injects via agent/pre-step as an independent user message block with its own project-context source tag (same mechanism as the skill catalog in dsh-tool-skill
• not spliced into the system prompt, no systemPrompt.context registration).
• Only sessions with a real cwd are treated as projects
• Per-session state lives in the session log (project-context/mode events, fold = last switch
• default ON), the same store sandbox/mode uses — no external state file, survives replay/export/checkpoint.