Import Claude Desktop MCP servers into Puffer

[shouc]

Summary

• implement puffer mcp add-from-claude-desktop for Claude Desktop stdio servers instead of printing a placeholder
• add --scope support to the command so imports can target user or workspace config
• skip Desktop servers that rely on per-server env blocks, since Puffer's current MCP manifest model cannot represent them yet, and report those skips explicitly

Audit scope

This was a fresh parity pass on latest master in a repo-local worktree after checking open PR scope first.

Explicitly excluded overlapping in-flight work:

• Document ignore-memory policy in the runtime prompt #23 audit/claude-parity-gaps-4 owns ignore-memory policy prompt guidance
• Load workspace and user memory into the runtime prompt #22 audit/claude-parity-gaps-3 owns runtime loading of workspace/user memory files
• Restore Claude-compatible /compact local command flow #21 audit/claude-parity-gaps-2 owns the /compact local-command parity fix
• Restore full Claude-compatible tool prompts for OpenAI #20 audit/claude-parity-gaps owns the OpenAI tool-prompt parity fixes

The concrete non-overlapping gap here was MCP CLI parity:

• Claude exposes mcp add-from-claude-desktop
• Puffer still printed Import from Claude Desktop is not implemented in Puffer yet.

Testing

• cargo test -p puffer-cli command_surface_desktop -- --nocapture
• cargo test -p puffer-cli mcp_add_from_desktop_accepts_scope_override -- --nocapture
• cargo test -p puffer-core mcp -- --nocapture

Notes

• The importer currently supports the subset of Claude Desktop MCP servers that Puffer can model today: stdio servers without per-server environment blocks.
• Servers with env are skipped and reported clearly rather than imported incorrectly.
• A full cargo test -p puffer-cli -- --nocapture run still hits an unrelated existing failure in authflow::tests::callback_listener_captures_matching_request on this machine; this PR does not touch authflow.
• For parity verification in the repo-local worktree, I temporarily mounted the existing local references/ corpus into the worktree so the audit could compare against the Claude reference tree. No references/ content is included in this branch.