fix(providers): limit Gemini CLI to legacy OAuth refresh (#8275)

#8232 correctly targeted OAuth auto-refresh for legacy stored Gemini CLI connections, but exceeded that compatibility goal by recreating a complete routable and UI-visible provider with an Antigravity model catalog.

Preserve legacy refresh by mapping gemini-cli rows to the existing Gemini OAuth credentials. Remove the public provider registry, OAuth preset, model routing snapshot, and canonical-provider tests while keeping Gemini API and Antigravity unchanged.

src/shared/constants/providers/oauth.ts

@@ -104,15 +104,6 @@ export const OAUTH_PROVIDERS = {
     subscriptionRisk: true,
     riskNoticeVariant: "oauth",
   },
-  "gemini-cli": {
-    id: "gemini-cli",
-    alias: undefined,
-    name: "Gemini CLI",
-    icon: "rocket_launch",
-    color: "#F59E0B",
-    subscriptionRisk: true,
-    riskNoticeVariant: "oauth",
-  },
   codex: {
     id: "codex",
     alias: "cx",