feat(retrieval): add time filters to find and search

[0xble]

Description

This PR adds native time filtering to retrieval. find and search can now
filter semantic results by created_at or updated_at through the Python SDK
and HTTP API, while the Rust CLI keeps a smaller --after / --before
surface.

OpenViking already stores these timestamps on indexed context records, but
retrieval could not query against them directly. This patch adds since,
until, and time_field to the retrieval surface, keeps the CLI mapping to
--after / --before only, and preserves created_at on rewrites so the
filters stay meaningful after reindex and update flows.

Related Issue

None.

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

• Added since, until, and time_field request fields to retrieval in the Python SDK, local client, HTTP server, and Rust HTTP client.
• Added a shared merge_time_filter() helper that compiles relative or absolute bounds into the existing metadata filter tree.
• Simplified the CLI down to ov find/search --after ... --before ..., which map to API since / until without the extra shortcut flags.
• Preserved created_at for leaf records on rewrite and reindex, and derived timestamps from canonical file metadata so created_at and updated_at keep stable semantics.
• Added server, unit, and CLI tests, and updated the English and Chinese retrieval docs.

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

Validation run locally on macOS:

• cargo test -p ov_cli --bin ov ✅
• uv run --isolated --with pytest --with pytest-asyncio python -m pytest tests/unit/test_search_filters.py tests/server/test_sdk_time_filters.py tests/server/test_api_search.py -q still fails on this host while importing pydantic_core with macOS code-signature validation (mapping process and mapped file (non-platform) have different Team IDs). That reproduces the earlier local environment issue even outside the repo .venv.

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)

Not applicable.

Additional Notes

I trimmed the CLI down after review feedback so the user-facing surface is just
--after / --before. If you would prefer an even smaller initial PR, I can
still split the write-path timestamp preservation from the retrieval API and
CLI surface.

[CLAassistant]

All committers have signed the CLA.

[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 3 🔵🔵🔵⚪⚪

🏅 Score: 90

🧪 PR contains tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ Recommended focus areas for review Missing License Header New file in openviking/ directory is missing the required AGPL-3.0 license header. from __future__ import annotations

[github-actions]

PR Code Suggestions ✨

No code suggestions found for the PR.

[MaojiaSheng]

I suggest just keep "--since, --until", and don't make it too complecated

[0xble]

Changed the CLI to --after / --before only because I think that is even simpler. The docs and local ov_cli test pass are updated to match.

[0xble]

Did one simplify pass on the current branch head. This only narrows the CLI helper to take the already-converted after / before string slices instead of borrowed Option<String> values; behavior stays the same.

[0xble]

Added one short comment in the time-filter merge helper and updated the checklist so the PR body matches the current branch state. Behavior is unchanged.