Local-first desktop workspace for ACP agents

Key features

• Backchat surfaces the capabilities, commands, models, modes, and permissions reported by the active harness instead of inventing a generic capability layer.
• ACP session and subagent model
• Sessions are grouped by their working directory, so files, terminals, browser state, and conversations stay attached to the project where the work happened.
• Projects can span related folders.
• One primary folder supplies the chat cwd, Git context, and project instructions