feat: add new model provider AtlasCloud

[imdm]

What this PR does

Before this PR:

• Users could not access AtlasCloud AI models within Cherry Studio

After this PR:

• AtlasCloud is now integrated as a native model provider. Users can easily select AtlasCloud from the provider list, use its default API endpoint, and configure their API keys with a dedicated brand icon.

Fixes #

Why we need it and why it was done in this way

AtlasCloud (https://atlascloud.ai) provides high-performance LLM inference services. Adding it as a native provider enhances Cherry Studio's ecosystem and provides more choices for users in specific regions or those requiring specific model capabilities.

The following tradeoffs were made:

• Used OpenAI-compatible API format
• I followed the existing provider implementation pattern
• No major architectural changes were introduced

The following alternatives were considered:

• Leaving users to use the "Custom OpenAI" provider. However, a dedicated provider improves UX by providing pre-set endpoints and brand recognition.

Breaking changes

None. This PR only adds a new feature and does not affect existing providers or data structures.

Special notes for your reviewer

• Logo asset included and properly configured
• Verified the API compatibility with AtlasCloud's current documentation

Checklist

This checklist is not enforcing, but it's a reminder of items that could be relevant to every PR.
Approvers are expected to review this list.

• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature.

Release note

Added AtlasCloud as a new model provider.

[YinsenHo]

pending