fix(frontend): correctly handle modelIDs containing slashes

[LazuliKao]

Summary

Problem

Model IDs that contain slashes (provider/namespace/model e.g., ollama/my-models/gemma4) were being truncated when sent in the request payload. This happened because the splitting logic in useSendPrompt used a limit of 2 when splitting the provider/model string, causing any secondary slashes to be discarded.

Changes

• Modified frontend/src/hooks/useOpenCode.ts: Updated useSendPrompt to correctly parse model strings with multiple slashes.

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation

Checklist

• Code follows project style (no comments, named imports)
• TypeScript types are properly defined
• Tests added/updated (80% coverage target)
• pnpm lint passes locally
• pnpm typecheck passes locally

[Copilot]

Pull request overview

Fixes frontend request payload construction so model IDs containing additional slashes (e.g., provider/namespace/model) are not truncated when sending prompts.

Changes:

• Update useSendPrompt model parsing to split on the first slash and preserve the remainder as modelID.

[Copilot]

Current validation only checks rest.length > 0, which allows inputs like "provider/" to send modelID: "" (and differs from existing parsing that checks !modelID). Consider computing const modelID = rest.join('/') and requiring providerID && modelID before setting requestData.model (to avoid empty/trailing-slash cases).

[Copilot]

PR description checklist says tests were added/updated, but this PR only changes useOpenCode.ts and doesn't include any test changes. Please either add/adjust tests for the model parsing behavior or update the PR description/checklist to match what was actually changed.