feat(cursor): add Cursor provider integration

[Knifelf]

Issue for this PR

Closes #25071

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds Cursor as a provider in OpenCode.

Changes in this PR:

• Adds Cursor provider integration for Cursor Cloud.
• Adds a Cursor option to opencode login with API key prompt flow.
• Adds dynamic model discovery via fetchCursorModelIds.
• Disables local tools for Cursor-backed sessions (Cursor runs tools in its own VM).
• Tracks active Cursor session with setActiveCursorSession.

Why this works:

• Login/auth flow now supports Cursor credentials.
• Provider model list comes from Cursor endpoint at runtime.
• Session/tool behavior is aligned with Cursor execution model to avoid tool conflicts.

How did you verify your code works?

• Ran opencode login and completed the new Cursor login flow.
• Authenticated with a valid Cursor API key and confirmed provider connection.
• Verified model discovery returns expected Cursor model IDs.
• Started a Cursor session and confirmed local tools are disabled for that session.

Screenshots / recordings

N/A (no UI changes)

Checklist

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

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