feat(cli): add model fallback system with provider priority

Implements intelligent model selection based on available providers.
Priority order: Native > Copilot > OpenCode Zen > Z.ai > Ultimate Fallback.

- Add model-fallback.ts with MODEL_CATALOG and capability-based resolution
- Extend InstallConfig with hasOpencodeZen and hasZaiCodingPlan
- Add TUI prompts and CLI args for new provider options
- Z.ai gets Librarian priority (zai-coding-plan/glm-4.7)

🤖 Generated with assistance of [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/cli/types.ts

@@ -6,6 +6,8 @@ export interface InstallArgs {
   claude?: ClaudeSubscription
   gemini?: BooleanArg
   copilot?: BooleanArg
+  opencodeZen?: BooleanArg
+  zaiCodingPlan?: BooleanArg
   skipAuth?: boolean
 }
 
@@ -14,6 +16,8 @@ export interface InstallConfig {
   isMax20: boolean
   hasGemini: boolean
   hasCopilot: boolean
+  hasOpencodeZen: boolean
+  hasZaiCodingPlan: boolean
 }
 
 export interface ConfigMergeResult {
@@ -28,4 +32,6 @@ export interface DetectedConfig {
   isMax20: boolean
   hasGemini: boolean
   hasCopilot: boolean
+  hasOpencodeZen: boolean
+  hasZaiCodingPlan: boolean
 }