feat: (poc) Unified AI Search

[Dnouv]

Proposed changes (including videos or screenshots)

• Introduce Unified Search Experience for AI search as a feature preview

Screen.Recording.2026-06-16.at.7.29.42.PM.mov

Issue(s)

Steps to test or reproduce

Further comments

• Metrics are planned to be introduced, following this PR.

AI-53

Summary by CodeRabbit

• New Features
  • Added native Intelligent Search to Rocket.Chat core, with unified results (rooms/users/messages) and optional AI-generated answers.
  • Enhanced NavBar search with an AI-assisted mode, inline filter chips, and intelligent suggestions.
  • Added an Intelligent Search page to explore sources and generate/regenerate answers.
  • Introduced an Admin AI Center to configure Intelligent Search and OpenAI-compatible LLM providers (including model listing).
• Bug Fixes
  • Fixed admin settings search to treat typed input as literal text (no accidental regex interpretation).
• Documentation
  • Added documentation comparing core vs Apps Engine Intelligent Search approaches.
• Tests
  • Added/updated coverage for unified search and AI answer flows.