fix(research): respect disabled web access

[alvin-cmd]

Summary

The web toggle only denied web_search and web_fetch, so the agent could still call trigger_research and reach the internet through a research job. This change adds trigger_research to the per-turn denylist when web access is off, while keeping explicitly requested research available. Regression tests cover both cases.

Target branch

• This PR targets dev, not main.

Linked Issue

Fixes #5527

Type of Change

• Bug fix (non-breaking, fixes a confirmed issue)
• New feature
• Breaking change
• Refactor / cleanup
• Documentation only
• CI / tooling / configuration

Checklist

• I searched open issues and open PRs. This is not a duplicate.
• This PR targets dev.
• My changes are limited to the issue. There are no unrelated refactors or whitespace changes.
• I ran the full app with Docker or Uvicorn. This policy-only change was verified with focused automated tests instead.

How to Test

1. Check out this branch in an existing Odysseus development environment.

2. Run the focused policy and research tests:

   python -m pytest tests/test_chat_route_tool_policy.py tests/test_tool_policy.py tests/test_research_chat_stream_owner.py -q

3. Confirm the suite reports 42 passing tests. The regression cases verify that trigger_research is denied when web access is off and remains available when research is explicitly enabled.

Visual / UI changes

Not applicable. This PR does not change CSS, HTML, SVG, or frontend JavaScript.