feat(search): validate responses against web results

Adds a post-generation validation step that checks whether a
search-grounded reply is actually supported by the retrieved
results: it extracts cited URLs from the response and flags
replies that claim to have searched without citing any of the
provided sources, as well as replies containing specific
numbers or dates absent from the results.

Also switches the default model to xiaomi/mimo-v2.6-flash and
documents the anti-hallucination behavior in the README.

README.md

@@ -7,7 +7,8 @@ A Telegram-based conversational AI agent that acts as a personal companion. It m
 - **Long-term memory**: User and agent profiles with auto-enrichment from conversations
 - **Daily routine management**: Schedule activities, meals, work/study times
 - **File workspace**: Create, edit, list and download files via natural language
-- **Web search**: Automatic or on-demand search for up-to-date information
+- **Web search**: Automatic or on-demand search for up-to-date information with hallucination validation
+- **Anti-hallucination**: Post-search validation ensures responses cite sources and don't invent facts
 - **Vision**: Image analysis with configurable vision models
 - **Voice**: Voice message transcription and response
 - **Proactive messaging**: Scheduled automatic messages based on daily routine