feat(codex): advance Codex/OpenAI model defaults to GPT-5.6 (Sol/Terra/Luna)

Update runtimeTierDefaults.codex and providerPresets.openai in
model-catalog.json to the GPT-5.6 family (gpt-5.6-sol/terra/luna),
advancing from the superseded GPT-5.4/5.5 generation.

Model IDs verified against OpenAI developer API docs:
- gpt-5.6-sol: flagship, /, reasoning xhigh
- gpt-5.6-terra: balanced, .50/, reasoning medium
- gpt-5.6-luna: fast/cheap, /, reasoning medium

Tier mapping is 1:1 (Sol↔flagship, Terra↔balanced, Luna↔fast),
so profile semantics are unchanged — only the underlying IDs advance.

Updates: catalog JSON, test assertions (catalog defaults), docs
(CONFIGURATION.md + zh-CN/pt-BR translations, workflow settings),
and changeset.

Closes #2122

gsd-core/workflows/settings.md

@@ -73,8 +73,8 @@ Parse current values (default to `true` if not present):
 ```
 Note: Quality, Balanced, Budget, and Adaptive profiles assign semantic tiers
 (Opus/Sonnet/Haiku) to each agent. When `runtime` is set in .planning/config.json,
-tiers resolve to runtime-native model IDs — on Codex that's gpt-5.5 / gpt-5.4 /
-gpt-5.4-mini with appropriate reasoning effort. See "Runtime-Aware Profiles" in
+tiers resolve to runtime-native model IDs — on Codex that's gpt-5.6-sol / gpt-5.6-terra /
+gpt-5.6-luna with appropriate reasoning effort. See "Runtime-Aware Profiles" in
 docs/CONFIGURATION.md.
 
 If `runtime` is unset on a non-Claude runtime, the profile tiers have no effect on