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advancing from the superseded GPT-5.4/5.5 generation.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

tests/commands.test.cjs

@@ -1204,7 +1204,7 @@ describe('resolve-model command', () => {
     assert.ok(result.success, `Command failed: ${result.error}`);
 
     const output = JSON.parse(result.output);
-    assert.strictEqual(output.model, 'gpt-5.5');
+    assert.strictEqual(output.model, 'gpt-5.6-sol');
     assert.strictEqual(output.profile, 'balanced');
     // #443: effort is now the unified field (xhigh for gsd-planner heavy tier default)
     assert.strictEqual(output.effort, 'xhigh');