Add local model compatibility guide

[karpizin]

Linked Issue

Closes #

Description

• Adds a new documentation page for local model compatibility in Mem0 OSS.
• Introduces a practical compatibility matrix covering:
  • Ollama as the recommended local path
  • LM Studio as supported with caveats
  • vLLM as supported for OpenAI-compatible self-hosted setups
  • smaller local instruct models as supported with caveats
• Explains when to choose each runtime and what tradeoffs to expect for self-hosted memory extraction.
• Links the new guide from the Open Source Features overview and the Python quickstart so local-model users can discover it early.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactor (no functional changes)
• Documentation update

Breaking Changes

N/A

Test Coverage

• I added/updated unit tests
• I added/updated integration tests
• I tested manually (describe below)
• No tests needed (explain why)

Manual verification:

• reviewed the new page in docs/open-source/features/local-model-compatibility.mdx
• verified that the new guide is linked from:
  • docs/open-source/features/overview.mdx
  • docs/open-source/python-quickstart.mdx
• checked that the content stays safely scoped to current main behavior and does not document not-yet-merged local-LLM enhancements

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have added tests that prove my fix/feature works
• New and existing tests pass locally
• I have updated documentation if needed