fix(subject): exclude redirected entries from /v0/subjects

[trim21]

Summary

• exclude redirected subjects (ield_redirect != 0) from subject browse/count queries
• prevent /v0/subjects from returning entries redirected to canonical subjects (e.g. to subject/2)
• add repository browse test assertions to ensure redirected entries are not returned

Testing

• existing pre-commit hooks passed (gofmt, go mod tidy)