Sparse-day-proof briefs, feed health check, and 16 new sources

- Briefs now fill from a rolling window (prefer today, backfill up to
  window_days) and exclude anything featured in the last 7 days of briefs, so
  slow days still produce five items without stories lingering day to day.
- New 'check-feeds' command fetches and parses every feed to catch dead ones.
- Added 16 validated sources (science, environment, animals, culture),
  expanding coverage from 12 to 28 feeds to reduce staleness.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

config/sources.toml

@@ -118,3 +118,147 @@ pr_risk_score = 4
 poll_interval_minutes = 120
 notes = "University research stories; watch PR framing."
 
+
+[[sources]]
+name = "Phys.org"
+feed_url = "https://phys.org/rss-feed/"
+default_category = "science"
+trust_score = 7
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Broad science aggregator."
+
+[[sources]]
+name = "Nature News"
+feed_url = "https://www.nature.com/nature.rss"
+default_category = "science"
+trust_score = 9
+pr_risk_score = 2
+poll_interval_minutes = 180
+notes = "Top-tier science journal news."
+
+[[sources]]
+name = "Ars Technica Science"
+feed_url = "https://feeds.arstechnica.com/arstechnica/science"
+default_category = "science"
+trust_score = 7
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Science/tech reporting."
+
+[[sources]]
+name = "The Guardian Science"
+feed_url = "https://www.theguardian.com/science/rss"
+default_category = "science"
+trust_score = 8
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Mainstream science; needs filtering."
+
+[[sources]]
+name = "The Guardian Environment"
+feed_url = "https://www.theguardian.com/environment/rss"
+default_category = "environment"
+trust_score = 8
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Environment; needs filtering."
+
+[[sources]]
+name = "ScienceDaily Plants & Animals"
+feed_url = "https://www.sciencedaily.com/rss/plants_animals.xml"
+default_category = "animals"
+trust_score = 6
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Animal/biology discoveries."
+
+[[sources]]
+name = "ScienceDaily Space & Time"
+feed_url = "https://www.sciencedaily.com/rss/space_time.xml"
+default_category = "science"
+trust_score = 6
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Space discoveries."
+
+[[sources]]
+name = "Smithsonian Magazine"
+feed_url = "https://www.smithsonianmag.com/rss/latest_articles/"
+default_category = "culture"
+trust_score = 7
+pr_risk_score = 3
+poll_interval_minutes = 180
+notes = "Culture, history, science human-interest."
+
+[[sources]]
+name = "Yale Environment 360"
+feed_url = "https://e360.yale.edu/feed.xml"
+default_category = "environment"
+trust_score = 8
+pr_risk_score = 2
+poll_interval_minutes = 180
+notes = "In-depth environment/solutions."
+
+[[sources]]
+name = "Anthropocene Magazine"
+feed_url = "https://www.anthropocenemagazine.org/feed/"
+default_category = "environment"
+trust_score = 7
+pr_risk_score = 3
+poll_interval_minutes = 180
+notes = "Sustainability solutions journalism."
+
+[[sources]]
+name = "The Conversation (US)"
+feed_url = "https://theconversation.com/us/articles.atom"
+default_category = "science"
+trust_score = 7
+pr_risk_score = 2
+poll_interval_minutes = 120
+notes = "Academic-authored explainers."
+
+[[sources]]
+name = "Colossal"
+feed_url = "https://www.thisiscolossal.com/feed/"
+default_category = "culture"
+trust_score = 6
+pr_risk_score = 3
+poll_interval_minutes = 240
+notes = "Art and visual culture."
+
+[[sources]]
+name = "Atlas Obscura"
+feed_url = "https://www.atlasobscura.com/feeds/latest"
+default_category = "culture"
+trust_score = 6
+pr_risk_score = 3
+poll_interval_minutes = 240
+notes = "Curiosities, places, culture."
+
+[[sources]]
+name = "New Scientist"
+feed_url = "https://www.newscientist.com/feed/home/"
+default_category = "science"
+trust_score = 7
+pr_risk_score = 3
+poll_interval_minutes = 120
+notes = "Science weekly."
+
+[[sources]]
+name = "ScienceAlert"
+feed_url = "https://www.sciencealert.com/feed"
+default_category = "science"
+trust_score = 6
+pr_risk_score = 4
+poll_interval_minutes = 120
+notes = "Pop science; watch hype."
+
+[[sources]]
+name = "Grist"
+feed_url = "https://grist.org/feed/"
+default_category = "environment"
+trust_score = 6
+pr_risk_score = 3
+poll_interval_minutes = 180
+notes = "Climate solutions reporting."