Remove member filtering from listing modes

[unitmatrix]

Summary

• make zget -l URL and zget -1 URL whole-archive listing modes only
• reject an extra MEMBER argument as a local usage error
• remove the CLI-side exact-name filter and not-found handling
• synchronize README, man page, and integration coverage

Why

zget_list() now intentionally streams the complete Central Directory. Keeping -l URL MEMBER in the CLI made exact-member listing a filter layered on top of a full directory scan, which conflicts with the minimal split between whole-archive listing and exact member extraction.

Behavior

zget [-o FILE] URL MEMBER
zget -l URL
zget -1 URL

Exact member selection remains the job of zget URL MEMBER; listing modes enumerate the archive.