feat(model): Add dedicated model provider

[xxx7xxxx]

Summary

• Currently, add models in the Agents Page since the Hub Page is unsuitable.
• Add a dedicated model-provider catalog backed by models.json(will also be merged into one file in the next work), with built-in CSGHub Lite, Codex, and Claude Code providers plus custom OpenAI-compatible providers.
• Add model-provider CRUD and connectivity-check APIs, and wire agent profiles to provider/model selectors so endpoints, keys, and model lists are managed centrally.
• Add the Web UI for browsing, creating, checking, editing, deleting, and selecting model providers across workspace and profile flows.

Screenshots

[RussellLuo]

The frontend changes in this PR currently conflict with a recently merged PR. Please rebase or merge the latest main and resolve the web/app conflicts before the next review pass.

[xxx7xxxx]

Conflict fixed