fix(cli): prefer mini-fast for install fallback

Default the install-time fallback chain to gpt-5.4-mini-fast for librarian and explore when OpenAI is available.\nKeep the snapshot and catalog tests aligned with the new resolution path.

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

src/cli/model-fallback.ts

@@ -127,7 +127,9 @@ export function generateModelConfig(config: InstallConfig): GeneratedOmoConfig {
   for (const [role, req] of Object.entries(CLI_AGENT_MODEL_REQUIREMENTS)) {
     if (role === "librarian") {
       let agentConfig: AgentConfig | undefined
-      if (avail.opencodeGo) {
+      if (avail.native.openai) {
+        agentConfig = { model: "openai/gpt-5.4-mini-fast" }
+      } else if (avail.opencodeGo) {
         agentConfig = { model: "opencode-go/minimax-m2.7" }
       } else if (avail.zai) {
         agentConfig = { model: ZAI_MODEL }
@@ -142,7 +144,9 @@ export function generateModelConfig(config: InstallConfig): GeneratedOmoConfig {
 
     if (role === "explore") {
       let agentConfig: AgentConfig
-      if (avail.native.claude) {
+      if (avail.native.openai) {
+        agentConfig = { model: "openai/gpt-5.4-mini-fast" }
+      } else if (avail.native.claude) {
         agentConfig = { model: "anthropic/claude-haiku-4-5" }
       } else if (avail.opencodeZen) {
         agentConfig = { model: "opencode/claude-haiku-4-5" }