Sources table: Media column (image coverage % + paywall marker)

Per Codex — make the table more decision-ready from data we already have.
Paywall is a domain-level hint, so it's a per-source flag (not a meaningful
rate): show image-coverage % plus a 🔒 marker for subscription domains in one
compact "Media" column (tooltip spells it out). source_health gains a
`paywalled` flag (is_paywalled on homepage/feed); also added to sources.csv.

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

goodnews/queries.py

@@ -11,6 +11,7 @@ import sqlite3
 from datetime import UTC, datetime, timedelta
 
 from .feeds import MAX_BACKOFF_MINUTES
+from .paywall import is_paywalled
 
 # Composite ranking used everywhere a "best first" order is needed. Kept as one
 # expression so brief, category feeds, and the API all rank identically.
@@ -332,6 +333,8 @@ def source_health(conn: sqlite3.Connection) -> list[dict]:
         # duplicate of content already served (accepted_total − served = accepted dupes).
         d["accepted_dup_rate"] = round(100 * (accepted - d["served"]) / accepted) if accepted else None
         d["image_coverage"] = round(100 * (d["images"] or 0) / d["served"]) if d["served"] else None
+        # Paywall is a domain-level hint, so it's a per-source flag (not a rate).
+        d["paywalled"] = is_paywalled(d.get("homepage_url") or d.get("feed_url"))
         # Match the REAL scheduler gate: due = the later of the streak-backoff time
         # and any retry_after_at rest (UTC strings sort chronologically).
         due_times = [t for t in (d["next_due_at"], d["retry_after_at"]) if t]