Read-time: full-article "Full story · ~N min" badge (Option B)

Replaces the gist-based read-time with the SOURCE article's full read time — the
contrast that sells the gist ("calm 1-min version here; ~10 min for the deep dive").

- goodnews/readtime.py: word_count_from_html (strips script/style/nav/header/
  footer/form/button/aside furniture before counting) + source_read_minutes
  (~225 wpm, 200-word floor, None when extraction looks failed/too thin).
- articles.source_words + read_checked_at columns (count only, never the body;
  fits the privacy posture). Idempotent migration.
- enrich.fetch_source_words + enrich_read_times: a bounded, retry-guarded cycle
  step (mirrors the image enrichers) that counts words for recent accepted
  articles. Only ever writes a real count; never overwrites good with zero. Wired
  into the cycle after recent-image enrichment.
- queries: source_words flows through _ARTICLE_COLUMNS; api exposes
  source_read_minutes on Article (null when unknown).
- home3: News card shows "Full story · ~N min", hidden entirely when null (no
  misleading "1 min").
- Tests: furniture stripping, threshold/rounding, enrich idempotency + no
  zero-overwrite, API null handling. 412 backend.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

goodnews/api.py

@@ -36,7 +36,7 @@ from fastapi.responses import FileResponse, HTMLResponse, RedirectResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel
 
-from . import art, auth, bloom, daily, email_send, feeds, games, oauth_google, onthisday, publishing, queries, quote, share, sources, summarize, wotd
+from . import art, auth, bloom, daily, email_send, feeds, games, oauth_google, onthisday, publishing, queries, quote, readtime, share, sources, summarize, wotd
 from .localtime import local_today
 from .markup import reply_html_to_text, sanitize_reply_html
 from .db import connect
@@ -322,6 +322,7 @@ class Article(BaseModel):
     paywalled: bool = False
     tags: list[str] = []
     summary: str | None = None  # our own cached summary (present on the brief)
+    source_read_minutes: int | None = None  # ~minutes to read the FULL source article (null = unknown)
     # Subject geography (present on feed rows; absent/empty on the brief). breadth is
     # locality|regional|national|multinational|global|unknown; places are ISO codes.
     geo_breadth: str | None = None
@@ -345,6 +346,7 @@ class Article(BaseModel):
             geo_confidence=row.get("geo_confidence"),
             geo_places=places,
             summary=row.get("summary"),
+            source_read_minutes=readtime.source_read_minutes(row.get("source_words")),
             id=row["id"],
             title=row["title"],
             description=row.get("description"),