docs: add Meganova provider

[bq1024]

Type of change

• Documentation

What does this PR do?

Adds Meganova provider documentation to the providers page. Meganova is a model aggregator providing access to open-weight models (DeepSeek, GLM, Kimi, MiniMax, Qwen, etc.) through a single API.

Provider data already available via models.dev#968 (merged).

How did you verify your code works?

Simple mdx change. Verified the section renders correctly in the local dev server.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Hey! Your PR title Add Meganova as a popular provider doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

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