[raymondginger2018-sudo]

Responds to the closing invitation on #269: "a small PR that adds a concern to
mcp list itself, for example an unpinned package (npx/uvx with @latest
or no version) or a server that receives credential environment variables."

Of those two examples the credential-env concern already exists on main
(cred -> sends-credential, merged via #241 / 2fafe40), so this PR adds the
remaining one: unpinned-package. It replaces #269's separate mcp audit
command with a concern on mcp list itself, as suggested.

What it does

mcp list now reports unpinned-package on a stdio server row when it is
launched through npx/uvx and its package argument floats -- no version at
all (npx -y left-pad) or a floating tag (npx -y left-pad@latest,
pkg@next). Those resolve whatever the registry serves at each start, so the
effective code was never chosen by the operator.

Recognition rules

command line	reading
npx -y left-pad	unpinned-package
npx -y left-pad@latest	unpinned-package
npx -y left-pad@next	unpinned-package
uvx mcp-server-time	unpinned-package
npx -y left-pad@1.2.3	pinned
uvx mcp-server-time==0.3.0	pinned (PEP 508)
npx @modelcontextprotocol/server-filesystem	unpinned (scoped name; the @ delimiter is only searched past position 0)
npx --index-url https://... pkg	flag/URL skipped; pkg is the package token
npx ./server.js, npx C:\x.js	local file -- no version to pin, not scanned
npx --version (flags only)	nothing to scan
python3 server.py	not a launcher, not scanned

• Windows launcher suffixes (.cmd/.exe/.bat/.ps1) are stripped before
  matching, so C:\Program Files\nodejs\npx.cmd -y left-pad is caught.
• Only the first package token decides; later positional arguments are the
  server's own operands (npx -y pkg /data).
• An optional leading v in the version (pkg@v1.2.3) counts as pinned.

Scope

• Reads only the existing command/args keys of mcp_server_view -- no
  serializer, McpServerInfo, or JSON-output change (consistent with how the
  existing concerns are table-only).
• Files: cli/mcp_cli.py (+65), tests/test_mcp_cli.py (+88); pure additions.

Testing

• New test_mcp_list_flags_unpinned_launcher_packages covers the rows above.
• tests/test_mcp_cli.py: 8 passed; pinned ruff 0.15.21 check + format clean;
  local CI preflight KNOWN-RED | new=0 (the 2 known reds are the documented
  Windows environment baselines: job-windows-lifecycle:group2_rc,
  job-desktop-quality:test_rc).