feat(onboard): add missing LLM providers and channels

[thieung]

Summary

• Add DashScope (Alibaba Cloud Coding Plan — Qwen API) and Bailian (Alibaba Cloud Model Studio) to onboard wizard with API key handling, env file export, and provider resolution
• Add Discord, Slack, WhatsApp, and Zalo Personal channels to onboard with credential prompts, validation, config application, and secret management
• Rename Feishu/Lark → Larksuite in channel options
• Bump filterThreshold from 5 → 10 so the 7-item channel list renders normally without type-to-filter mode

Changes

cmd/onboard.go: Add 2 providers to providerMap + providerOptions, add 4 channels to selection/pre-fill/validation/config/secrets/summary
cmd/onboard_helpers.go: Add dashscope/bailian cases in applyProviderAPIKey(), add Discord/Slack env vars in onboardWriteEnvFile()
cmd/onboard_resolve.go: Add dashscope/bailian cases in resolveProviderAPIKey() + resolveProviderAPIBase()
cmd/prompt.go: Bump filterThreshold 5 → 10

Test plan

• Run ./goclaw onboard and verify all 15 providers appear in selection
• Verify all 7 channels appear and can be toggled with space/x
• Select Discord/Slack/WhatsApp and verify credential prompts appear
• Verify .env.local contains correct env vars for new providers/channels
• Verify config.json does not contain secrets for new channels

[viettranx]

Review: Request Changes

Critical: PR is unmergeable — stale branch

This PR was branched before 3187196 (refactor(onboard): simplify to DB + keys only, delegate setup to web UI), which removed the full onboard wizard. Current main has a simplified onboard.go (~177 lines, DB+keys only) and delegates provider/channel setup to the web UI.

Files affected:

• cmd/onboard.go — completely rewritten on main (old wizard removed)
• cmd/onboard_resolve.go — deleted on main
• cmd/onboard_helpers.go — signature changed (onboardWriteEnvFile now takes (path, dsn, token, key))

Recommended approach: Instead of the full wizard, add new providers/channels to cmd/onboard_managed.go → defaultPlaceholderProviders (same pattern as PR #102 for Z.ai). Channel config is now handled via the web UI.

---

Bug: DashScope API base URL wrong region

In resolveProviderAPIBase():

case "dashscope":
    return "https://dashscope.aliyuncs.com/compatible-mode/v1"

Should be https://dashscope-intl.aliyuncs.com/compatible-mode/v1 (with -intl), matching gateway_providers.go and onboard_managed.go.

---

Minor issues

1. Zalo Personal — no credential prompt, no validation. Every other channel has both. If it needs credentials at runtime, this silently fails.

2. WhatsApp bridge URL not exported to .env.local — Discord/Slack tokens are written to env file, but WhatsApp's BridgeURL is not. Inconsistent.

---

Please rebase onto current main and adapt to the new onboard architecture. Happy to help if you have questions about the new structure!

[thieung]

New refactor PR #126