feat: wire MegaNova into onboard wizard

[bq1024]

Summary

• Adds meganova-api-key as a selectable auth choice in the interactive onboard wizard
• Adds --meganova-api-key CLI flag for non-interactive onboarding
• Adds MegaNova to auth choice groups, preferred provider mapping, and auth inference

Files changed

• src/cli/program/register.onboard.ts — pass meganovaApiKey from CLI opts
• src/commands/auth-choice-options.ts — add MegaNova group and option
• src/commands/auth-choice.apply.api-providers.ts — interactive auth flow
• src/commands/auth-choice.preferred-provider.ts — provider mapping
• src/commands/onboard-non-interactive/local/auth-choice.ts — non-interactive flow
• src/commands/onboard-non-interactive/local/auth-choice-inference.ts — type fix
• src/commands/onboard-provider-auth-flags.ts — CLI flag definition

Test

openclaw onboard --non-interactive --mode local --auth-choice meganova-api-key --meganova-api-key "$MEGANOVA_API_KEY" --accept-risk

Verified: config written with meganova:default auth profile, all 38 models registered, default model set to meganova/zai-org/GLM-5.