FN-7716: stop requiring a Fusion-visible API key for Grok CLI provider

Grok CLI provider readiness now mirrors the Cursor CLI provider: it is derived from the `grok` binary being available rather than requiring a Fusion-visible GROK_API_KEY or ~/.grok/user-settings.json, since the CLI manages its own auth.

- probeGrokBinary now derives `authenticated` from binary availability (readiness) instead of API-key/user-settings presence; key detection surfaces as a non-blocking `apiKeyDetected` hint
- /auth/status treats the grok-cli provider as authenticated when enabled + binary available
- GrokCliProviderCard drops the blocking "Set GROK_API_KEY" state
- Direct xAI streaming path is unchanged and still uses $GROK_API_KEY when present (FN-7711/FN-7714)
- Added changeset for @runfusion/fusion (patch)

Files changed:
$(cat /tmp/diffstat_fn7716.txt)

Fusion-Task-Id: FN-7716

Fusion-Task-Lineage: ac0efc79-2510-465e-9cd2-4938c08989c9

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

packages/dashboard/app/api/legacy.ts

@@ -1971,7 +1971,10 @@ export interface CursorCliStatus {
 export interface GrokCliStatus {
   binary: {
     available: boolean;
+    /** FNXC:GrokCli 2026-07-09-00:00: FN-7716 — "ready" (binary available), not "key present"; the grok CLI owns auth. */
     authenticated?: boolean;
+    /** FNXC:GrokCli 2026-07-09-00:00: FN-7716 — non-blocking informational hint that Fusion detected a Grok API key. Never gates readiness. */
+    apiKeyDetected?: boolean;
     version?: string;
     binaryPath?: string;
     configuredBinaryPath?: string;