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/index.ts

@@ -19,6 +19,7 @@ import { registerGdocsAuthCommand } from './gdocs-auth.js';
 import { registerGdriveAuthCommand } from './gdrive-auth.js';
 import { registerGtasksAuthCommand } from './gtasks-auth.js';
 import { registerOpenaiAuthCommand } from './openai-auth.js';
+import { registerZaiAuthCommand } from './zai-auth.js';
 import { registerSkillsCommand } from './skills.js';
 
 export function createProgram(): Command {
@@ -43,6 +44,7 @@ export function createProgram(): Command {
   registerGdriveAuthCommand(program);
   registerGtasksAuthCommand(program);
   registerOpenaiAuthCommand(program);
+  registerZaiAuthCommand(program);
   registerSkillsCommand(program);
 
   return program;