feat: add DeepResearch support to session tools

[wsp1911]

Summary

Add DeepResearch as an allowed agent type for the SessionControl and SessionMessage tools.

The existing agentic, Plan, and Cowork agent types remain supported.

Type and Areas

Type:

Feature

Areas:

Rust core, Agent Runtime

Motivation / Impact

This enables agents to create and message DeepResearch sessions through the session tools.

The new agent type is available in:

• Tool descriptions.
• Input schemas.
• Session message deserialization.
• Session control runtime contracts.

DeepResearch also supports the existing canonical name and lowercase aliases.

Verification

• cargo test --locked -p bitfun-agent-runtime --test agent_session_contracts session_control_contracts
  • 6 passed.
• cargo test --locked -p bitfun-core --no-default-features --features agent-runtime --lib agentic::tools::implementations::session_
  • 24 passed.
• git diff --cached --check
  • Passed.

Reviewer Notes

• Plan and Cowork remain available.
• DeepResearch is exposed as DeepResearch with deepresearch and DEEPRESEARCH deserialization aliases.
• No UI changes or manual UI verification were required.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.