feat(models): add Z.AI (GLM) credential integration and setup flow

Implement first-class Z.AI credential storage and authentication:

- New auth provider: src/auth/zai.ts for Z.AI API key management
- New CLI command: flynn zai-auth to store Z.AI API keys
- New TUI command: /login zai for interactive credential entry
- Modified src/auth/index.ts to register zai provider
- Modified src/cli/index.ts to register zai-auth command
- Modified src/cli/setup/providers.ts to include Z.AI in setup wizard
- Modified src/daemon/models.ts to support zhipuai use_oauth flag
- Modified src/daemon/clientFactory.test.ts to add Z.AI tests
- Modified src/frontends/tui/commands.ts to add login command
- Modified src/frontends/tui/minimal.ts to support credential prompts

This allows users to authenticate with Z.AI (GLM models) without
embedding secrets in config files. Credentials are stored securely in
~/.config/flynn/auth.json and resolved at runtime.

Updated state.json with new feature entry documenting the integration.

src/cli/setup/providers.ts

@@ -21,6 +21,7 @@ const TOP_TIER: ProviderDef[] = [
 const SECOND_TIER: ProviderDef[] = [
   { name: 'Gemini', provider: 'gemini', defaultModel: 'gemini-2.5-flash', fastModel: 'gemini-2.0-flash-lite', needsApiKey: true, needsEndpoint: false, apiKeyLabel: 'Gemini API key' },
   { name: 'OpenRouter', provider: 'openrouter', defaultModel: 'anthropic/claude-sonnet-4', needsApiKey: true, needsEndpoint: false, apiKeyLabel: 'OpenRouter API key' },
+  { name: 'Z.AI (GLM)', provider: 'zhipuai', defaultModel: 'glm-4.7', needsApiKey: true, needsEndpoint: true, defaultEndpoint: 'https://api.z.ai/api/paas/v4', apiKeyLabel: 'Z.AI API key' },
   { name: 'xAI (Grok)', provider: 'xai', defaultModel: 'grok-3', fastModel: 'grok-3-mini', needsApiKey: true, needsEndpoint: false, apiKeyLabel: 'xAI API key' },
   { name: 'Amazon Bedrock', provider: 'bedrock', defaultModel: 'anthropic.claude-sonnet-4-20250514-v1:0', needsApiKey: false, needsEndpoint: false },
   { name: 'GitHub Models', provider: 'github', defaultModel: 'claude-sonnet-4-20250514', needsApiKey: false, needsEndpoint: false },
@@ -32,6 +33,7 @@ const PROVIDER_HELP: Record<string, string> = {
   ollama: 'Ollama runs locally — install from https://ollama.com and run: ollama serve',
   gemini: 'Get your API key at https://aistudio.google.com/apikey',
   openrouter: 'Get your API key at https://openrouter.ai/keys (supports 200+ models)',
+  zhipuai: 'Get your API key at https://z.ai/manage-apikey/apikey-list (Coding Plan endpoint: https://api.z.ai/api/coding/paas/v4)',
   xai: 'Get your API key at https://console.x.ai',
   bedrock: 'Uses AWS credentials from environment (~/.aws/credentials or IAM role)',
   github: 'Uses GitHub Copilot — authenticate via OAuth device flow on first use',