fix: digest content hierarchy, dedup, and inclusive tone

[bokelley]

Summary

• Cap articles at 5 total (2 official + 3 external max, was 7)
• LLM selects top 3 external articles (was 5)
• From the Inside: only show WGs with meetings or threads (not just new member joins)
• WG summary uses most interesting content item (meeting recap or thread), not mission statement
• New member joins alone no longer qualify a WG for inclusion (was showing 12 groups, most with just "X new members joined")

Test plan

After deploy, hit Regenerate on /admin/digest. Should see:

• 5 items max in Worth Your Time
• Only 3-4 WGs in From the Inside (Editorial, Media Buying, Governance, Creative)
• No groups showing just "X new members joined"

🤖 Generated with Claude Code