fix(ci): genericize brain fixture in vendored suite (sanitization gate)

The BRAIN example fixture carried the operator's forge namespace
(jason.woltje/mosaic-brain) — operator-identity token on the public
denylist, caught by the sanitization gate in pipeline 2629. Replaced
with a generic example.invalid owner; same direct-flow shape. Suite
101/101 green; sanitization gate green.

packages/mosaic/framework/tools/structure/test-validate-repo-json.sh

@@ -49,7 +49,7 @@ expect_err_notrace() { # like expect_err, plus no traceback anywhere in output
 }
 
 STACK='{"schema_version":2,"integration_trunk":"next","release_branch":"main","flow":"trunk-release","canonical_remote":"https://git.mosaicstack.dev/mosaicstack/stack","canonical_clone":"host:/src/mosaic-stack","worktree_root":"host:/src/mosaic-stack-worktrees","worktree_policy":"orchestrator-precreated","notes":"x"}'
-BRAIN='{"schema_version":2,"integration_trunk":"main","release_branch":"main","flow":"direct","canonical_remote":"https://git.mosaicstack.dev/jason.woltje/mosaic-brain","canonical_clone":"host:/.mosaic","worktree_root":"host:/.mosaic-worktrees","worktree_policy":"orchestrator-precreated"}'
+BRAIN='{"schema_version":2,"integration_trunk":"main","release_branch":"main","flow":"direct","canonical_remote":"https://git.example.invalid/acme/brain","canonical_clone":"host:/.mosaic","worktree_root":"host:/.mosaic-worktrees","worktree_policy":"orchestrator-precreated"}'
 ROOT="$SB/hostroot"; mkdir -p "$ROOT"
 
 echo "== (0) syntax + version =="