fix(cli): check and run imports with trailing comments in checkup

[oxura]

Fixes #1497.

A valid import ./bad.bend as Bad # comment checks the imported file normally, but --checkup treated it as a non-import: it exited 0 without any check/run. Good commented imports were skipped too. Accept the language's trailing # comment in the existing checkup import matcher; do not change the language parser or independent per-module execution.

The new permanent installed-CLI assertion checks both consequences: a commented bad import exits 1, and a commented good import actually runs and returns 5n. Existing uncommented checkup/closed-reader controls remain. The exact new assertion fails on unchanged source behavior and passes with the real rebuilt standalone CLI. No diagnostic wording or implementation-source assertions. README documents aliased checkup imports; hand-written GUIDE/CHANGELOG are unchanged.

Actual Linux x64 verification:

• Before: the ordinary checker accepts the good aggregation syntax and rejects the bad module, while both commented checkups incorrectly return 0 with empty output.
• Twenty real source/compiled CLI checkup executions cover good/bad comments, original plain imports, comments immediately after the alias, CRLF, a commented-out nonexistent import, a real missing import, an absolute path, and a mixed failing-then-good aggregation. Failures remain nonzero and the mixed aggregation still runs the good module.
• Exact permanent assertion executed fail-before/pass-after using real CLI processes.
• Standalone CLI rebuilt from this branch.
• bun gates/repo.ts: 54/54; permanent caps and gate policy unchanged.

Full installer/archive/hub ping was not run because the sibling site checkout is unavailable; isolated assertion proof is not a claim that the full ping gate passed.