docs: update README memory search API example for v1 search endpoint

[CZH-THU]

Description

Update the README documentation to reflect the current v1 memory search API request format.

Type of Change

• Documentation update

Related Issues

Fixes #
Relates to #

Changes Made

• Replaced the outdated /api/v1/memories/search example that used GET/query-string style syntax
• Updated the README example to use POST with JSON body matching SearchMemoriesRequest
• Included current fields such as method, memory_types, and structured filters

Testing

• Tested locally with manual verification
• Added/updated unit tests
• Added/updated integration tests
• All existing tests pass

Test Configuration:

• OS: Windows
• Python version: N/A for docs change
• Database versions (if relevant): N/A

Test Results:

Verified README example against current endpoint schema and local code comment/reference

Checklist

• My code follows the project's code style guidelines
• I have performed a self-review of my code
• I have commented my code where necessary, particularly in complex areas
• I have updated the documentation accordingly
• My changes generate no new warnings or errors
• 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 used Gitmoji in my commit messages
• Any dependent changes have been merged and published

Additional Notes

This PR only updates documentation and does not modify runtime code or API behavior.

Breaking Changes

None.