feat(model-requirements): prefer GPT-5.4 and glm-5 in agent fallback chains

Align Prometheus, Momus, and Atlas with newer GPT-5.4 fallback tiers and replace Sisyphus install-time GLM-4.7 fallbacks with GLM-5 only.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/model-requirements.test.ts

@@ -145,19 +145,19 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
     expect(primary.variant).toBe("max")
   })
 
-  test("momus has valid fallbackChain with gpt-5.2 as primary", () => {
+  test("momus has valid fallbackChain with gpt-5.4 as primary", () => {
     // given - momus agent requirement
     const momus = AGENT_MODEL_REQUIREMENTS["momus"]
 
     // when - accessing Momus requirement
-    // then - fallbackChain exists with gpt-5.2 as first entry, variant medium
+    // then - fallbackChain exists with gpt-5.4 as first entry, variant xhigh
     expect(momus).toBeDefined()
     expect(momus.fallbackChain).toBeArray()
     expect(momus.fallbackChain.length).toBeGreaterThan(0)
 
     const primary = momus.fallbackChain[0]
-    expect(primary.model).toBe("gpt-5.2")
-    expect(primary.variant).toBe("medium")
+    expect(primary.model).toBe("gpt-5.4")
+    expect(primary.variant).toBe("xhigh")
     expect(primary.providers[0]).toBe("openai")
   })
 
@@ -174,6 +174,10 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
     const primary = atlas.fallbackChain[0]
     expect(primary.model).toBe("claude-sonnet-4-6")
     expect(primary.providers[0]).toBe("anthropic")
+
+    const secondary = atlas.fallbackChain[1]
+    expect(secondary.model).toBe("gpt-5.4")
+    expect(secondary.variant).toBe("medium")
   })
 
   test("hephaestus supports openai, github-copilot, venice, and opencode providers", () => {