docs(examples): retire legacy integration examples

[qin-ctx]

Description

Retire legacy example integrations that no longer match the current OpenViking server and MCP design, and refresh the basic usage example so it points at the supported configuration, server, and MCP flows.

Related Issue

N/A

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 not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Remove the deprecated examples/mcp-query, examples/server_client, and examples/misc example paths.
• Rewrite examples/basic-usage documentation to reflect the current SDK, server-mode, and MCP guidance.
• Update examples/basic-usage/basic_usage.py so the example flow matches current client behavior more reliably.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Manual validation:

• Ran python -m py_compile examples/basic-usage/basic_usage.py
• Verified stale example references were removed from active example docs

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

• examples/opencode/plugin was intentionally kept in place.
• An unrelated unstaged local deletion of examples/claude-memory-plugin/README_CN.md was left out of this PR.

[github-actions]

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