fix: improve Addie thread conversation flow

[bokelley]

Summary

Two improvements to Addie's conversational behavior in Slack threads:

• Auto-respond in active threads: When a user replies to a thread where Addie has already participated, Addie now responds automatically without requiring an explicit @mention. This creates natural conversation flow - users can say "Yes please" to Addie's follow-up questions without needing to @mention her again.

• Conversation history for @mentions: Addie now remembers what she said in previous @mention interactions. Previously, she only had access to other users' messages in the thread (not her own), which caused hallucinations where she would confabulate what she had previously said/done.

Implementation Details

• Added checkAddieThreadParticipation() to detect Addie's presence in threads (returns both participation status and messages to avoid duplicate API calls)
• Added handleActiveThreadReply() to handle implicit mentions in active threads
• Added conversation history fetching to handleAppMention() for Claude context
• Added conversation history fetching to handleActiveThreadReply() as well

Test plan

• Test replying to a thread where Addie has already responded - should auto-respond without @mention
• Test replying to a thread where Addie has NOT responded - should NOT auto-respond (goes through router)
• Test @mention in a thread - Addie should remember her previous responses accurately
• Build and unit tests pass

🤖 Generated with Claude Code