fix(glaz): adopt upstream relationships proto relocation

What

Adopt the upstream fix (glaz!93) for the relationships-proto descriptor collision, instead of a downstream workaround.

Both contracts carried the descriptor path proto/relationships/relationships.proto; Go's proto registry keys by path (not package), so init panicked once both clients linked into one binary. glaz!93 relocated the GLAZ descriptor under proto/glaz/ at the source.

Changes

• Bump vendir.yml to the auth/glaz commit including glaz!93; vendir sync pulls the relocated proto (import updated upstream).
• Regenerate: stubs move to gen/glaz/proto/glaz/relationships/; internal/authz/glaz import paths updated (exercised by the existing glaz tests).
• scripts/proto-generate.sh reverts to the plain buf generate — no more ephemeral staging-rewrite.
• Docs: note the relocation + a gotcha (vendir sync deletes the AR-owned buf.yaml/buf.gen.yaml, which must be restored after sync).

Testing

go build ./..., the internal/authz/glaz tests, and the generation freshness check are green.

Related to gitlab-org/gitlab#605903 (closed)