feat(cli): expand Cursor host mounts, Sandcat-controlled CLI config, and workspace isolation

[wiacekm]

Summary

Align Sandcat devcontainers with Cursor CLI host configuration: mount shared customization from ~/.cursor/, persist this sandbox's runtime state without leaking other workspaces, and manage Cursor CLI keys through Sandcat settings instead of bind-mounting cli-config.json.

• Mount additional Cursor host paths when SANDCAT_MOUNT_CURSOR_CONFIG=true: commands/, hooks.json, hooks/, agents/, and mcp.json (read-only), alongside existing AGENTS.md, rules/, and skills/
• Pre-create missing host bind sources on sandcat init (directories via mkdir, JSON files with minimal valid defaults) so Docker mounts files instead of root-owned empty directories
• Add Sandcat-controlled Cursor CLI config via cursor.cli in settings: mitmproxy merges settings layers, writes /mitmproxy-config/cursor-cli-config.json, and the agent deep-merges that fragment into cli-config.json in agent-home on startup (Sandcat keys win; Cursor-managed keys persist in the volume). Default cursor.cli.network.useHttp1ForAgent: true for mitmproxy stability
• Scope runtime state to the current workspace only: mount ~/.cursor/projects/workspaces-<project-name>/ read-write; keep chats/, plugins/, and subagents/ in agent-home so other workspaces' Cursor data is not exposed
• Document optional volume mount customization (all-or-nothing init flags, per-path compose editing, Claude vs Cursor path tables, isolation notes)

Test plan

• cd cli && bats test/agents/agents.bats test/composefile/composefile.bats test/init/init.bats test/init/regression.bats test/init/user_settings.bats
• cd cli && pytest test/mitmproxy/test_mitmproxy_addon.py -k cursor_cli
• sandcat init --agent cursor --name myproject and verify compose mounts only projects/workspaces-myproject/
• Rebuild devcontainer; confirm host ~/.cursor/rules/ etc. appear read-only in the agent
• Confirm cli-config.json in agent-home receives useHttp1ForAgent from Sandcat settings without a host bind mount
• Confirm agent cannot list other workspaces under ~/.cursor/projects/ or access host chats/, plugins/, subagents/