docs: clarify session_search auxiliary model docs

[YanzhongSu]

What does this PR do?

Updates stale session_search docstrings that said session summarization uses Gemini Flash.

Current behavior routes session search summarization through the configured auxiliary.session_search model. With the default provider: "auto" setting, this uses the main chat provider/model unless the user explicitly overrides the auxiliary task. The updated wording matches the current auxiliary model routing behavior and avoids implying that Gemini Flash is always used.

Related Issue

No issue filed.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• Updated the module docstring in tools/session_search_tool.py to describe the configured auxiliary session_search model instead of a hardcoded Gemini Flash model.
• Updated the session_search() function docstring in tools/session_search_tool.py with the same corrected model-routing language.

How to Test

1. Inspect tools/session_search_tool.py.
2. Confirm the docstrings refer to the configured auxiliary session_search model.
3. Confirm there are no remaining Gemini Flash references in tools/session_search_tool.py.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Screenshots / Logs

N/A. Docstring-only change.

[teknium1]

Salvaged via #19593 onto current main - your commit authorship was preserved. Thanks!