fix(model-requirements): add github-copilot to hephaestus requiresProvider

Hephaestus requires GPT models, which can be provided by github-copilot.
The requiresProvider list was missing github-copilot, causing hephaestus
to not be created when github-copilot was the only GPT provider connected.

This also fixes a flaky CI test that documented this expected behavior.

src/shared/model-requirements.ts

@@ -24,9 +24,9 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
   },
   hephaestus: {
     fallbackChain: [
-      { providers: ["openai", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
+      { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.3-codex", variant: "medium" },
     ],
-    requiresProvider: ["openai", "opencode"],
+    requiresProvider: ["openai", "github-copilot", "opencode"],
   },
   oracle: {
     fallbackChain: [