fix(#2406): stop Codex config.toml from double-registering agent roles (#2432)

* fix(#2406): stop Codex config.toml from double-registering agent roles

generateCodexConfigBlock emitted an [agents.<name>] role table per agent
pointing config_file back at the standalone agents/<name>.toml Codex
already auto-discovers, so every install declared each role twice in
one config layer and Codex logged a duplicate-role warning per agent.
Remove the redundant role-table loop; the standalone per-agent TOML is
now the sole canonical registration source. The existing marker-truncate
and leaked-section stripping in mergeCodexConfig already clean up legacy
[agents.gsd-*] tables from prior installs, so updates converge to zero
duplicates without any new migration path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#2406): regenerate fixtures + lint gate-prep

* fix(#2406): repair failing tests after gate verification

* docs(#2406): add changeset for Codex duplicate agent-role fix

Adds the missing .changeset/*.md fragment for the Codex config.toml
double-registration fix, closing the PR-gate finding from review.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#2406): backfill changeset pr (#2432)

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests/fixtures/golden-install-parity/codex.json

@@ -140,7 +140,7 @@
   "agents/gsd-user-profiler.toml": "b9c244bb8fbf8140",
   "agents/gsd-verifier.md": "4ac4b860e2504374",
   "agents/gsd-verifier.toml": "8ed9fb961409e894",
-  "config.toml": "b5f627b42f060910",
+  "config.toml": "aa0b484a070f603c",
   "gsd-core/.gsd-runtime": "243b0dc9b847e66c",
   "gsd-core/VERSION": "ef0deccd81a6723c",
   "gsd-core/bin/check-latest-version.cjs": "e4a224058c8f4d74",