fix: forward resolved context limit to Ollama

[zerone0x]

Description

This PR fixes the missing runtime half of #485 for Ollama-backed models.

Nanocoder already let users configure context limits via:

• /context-max / --context-max
• provider-level contextWindow
• per-model contextWindows
• subagent contextWindow

But those limits were only used inside Nanocoder for context accounting and auto-compact decisions. They were not being forwarded to Ollama itself, so the actual model runtime could still use a different context size.

This change now forwards the resolved Nanocoder context limit to Ollama as options.num_ctx on each request, so the configured limit affects the real runtime behavior too.

It also updates the docs to make that behavior explicit.

Type of Change

• New feature
• Bug fix
• Breaking change
• Documentation update

Testing

Automated Tests

• New features include passing tests in .spec.ts/tsx files
• All existing tests pass (pnpm test:all completes successfully)
• Tests cover both success and error scenarios

Ran:

• npm exec --yes pnpm -- test:ava source/ai-sdk-client/chat/provider-options.spec.ts
• npm exec --yes pnpm -- test:types
• npm exec --yes pnpm -- exec biome check source/ai-sdk-client/chat/provider-options.ts source/ai-sdk-client/chat/provider-options.spec.ts source/ai-sdk-client/chat/chat-handler.ts docs/configuration/providers/ollama.md docs/features/subagents.md

Manual Testing

• Tested with Ollama
• Tested with OpenRouter
• Tested with OpenAI-compatible API
• Tested MCP integration (if applicable)

Manual testing was not run in this environment.

Checklist

• Code follows project style guidelines
• Self-review completed
• Documentation updated (if needed)
• No breaking changes (or clearly documented)
• Appropriate logging added using structured logging

Closes #485