Fix CloudSigma tag collection endpoint

[rjcloudsigma]

Summary

Correct CloudSigma API v2 ex_list_tags() to use the documented /tags/ collection instead of /tags/detail/.

Update the existing mock collection handler to return the GET fixture while retaining POST behavior. Reject the obsolete detail mock route to catch regressions. No converter, authentication, method signature or native pagination behavior changes.

Verification

• 148 applicable CloudSigma v1/v2 unittest cases passed on Python 3.12.3; zero failures, errors or skips, with Python socket/process dispatch denied during the mock suite.
• Project filename and ASF license-header checks passed; isolated environment pip check passed.
• Applicable dependencies pinned and verified against official PyPI wheel hashes, including requests-mock 1.12.1 and requests 2.34.2.
• A separately bounded actual NEXT candidate read returned HTTP200 and an empty tag list after authenticated profile admission. The test harness explicitly rewrote native limit=0 to limit=1; this is not native pagination or complete enumeration qualification.

The original diagnostic observed HTTP404 on /tags/detail/; the public collection example documents /tags/. These are scoped observations, not universal endpoint guarantees.

Scope limits

No full-repository suite, all-Python-version matrix, populated live-tag conversion, full driver-family qualification or release readiness is claimed. Synthetic credentials, environments, wheels and evidence are excluded from this change.