Add feed/reader mode with full-article capture at ingest

Reader mode presents the stories on a page one at a time in a focused
overlay, marking each read as it's shown. Left/right arrows (or the header
book button / `f`) page through them; read stories dim on the grid. Read
state is device-local in localStorage.

Backing this required actually capturing article bodies, which Pete wasn't
doing — it kept only the RSS <description> lede and discarded content:encoded:

- stories.content column (idempotent migration; old rows fall back to lede)
- parser keeps content:encoded as paragraph-preserving text
- article fetch already done for paywall detection now also returns its body,
  so ingest stores the richer of feed-content vs scraped body with no extra
  request (prefers the archive snapshot body for paywalled stories)
- GET /api/article?id= serves the stored text; card queries now select id and
  expose it as data-id for the reader

Tests cover content extraction, the storage round-trip, and the article
endpoint + card rendering end to end.

internal/storage/storage_test.go

@@ -61,6 +61,67 @@ func TestInsertStoryAndGUIDSeen(t *testing.T) {
 	}
 }
 
+func TestGetStoryReaderText(t *testing.T) {
+	setupTestDB(t)
+
+	s := &Story{
+		GUID:       "reader-guid",
+		Headline:   "Reader Headline",
+		Lede:       "Short lede.",
+		Content:    "First paragraph.\n\nSecond paragraph.",
+		ArticleURL: "https://example.com/reader",
+		Source:     "Src",
+		SeenAt:     1700000000,
+	}
+	if err := InsertStory(s); err != nil {
+		t.Fatal(err)
+	}
+	var id int64
+	if err := Get().QueryRow(`SELECT id FROM stories WHERE guid = ?`, s.GUID).Scan(&id); err != nil {
+		t.Fatal(err)
+	}
+
+	content, lede, found, err := GetStoryReaderText(id)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !found {
+		t.Fatal("expected story to be found")
+	}
+	if content != s.Content {
+		t.Errorf("content = %q, want %q", content, s.Content)
+	}
+	if lede != s.Lede {
+		t.Errorf("lede = %q, want %q", lede, s.Lede)
+	}
+
+	// A story ingested before content capture (no content) is still found, with
+	// an empty content string so the reader falls back to the lede.
+	bare := &Story{GUID: "bare-guid", Headline: "H", Lede: "Only a lede.", ArticleURL: "https://a.com", Source: "S", SeenAt: 1}
+	if err := InsertStory(bare); err != nil {
+		t.Fatal(err)
+	}
+	var bareID int64
+	if err := Get().QueryRow(`SELECT id FROM stories WHERE guid = ?`, bare.GUID).Scan(&bareID); err != nil {
+		t.Fatal(err)
+	}
+	content, lede, found, err = GetStoryReaderText(bareID)
+	if err != nil || !found {
+		t.Fatalf("bare story: found=%v err=%v", found, err)
+	}
+	if content != "" {
+		t.Errorf("bare content = %q, want empty", content)
+	}
+	if lede != "Only a lede." {
+		t.Errorf("bare lede = %q", lede)
+	}
+
+	// Unknown id reports not-found rather than erroring.
+	if _, _, found, err = GetStoryReaderText(999999); err != nil || found {
+		t.Errorf("unknown id: found=%v err=%v, want found=false err=nil", found, err)
+	}
+}
+
 func TestInsertStoryDuplicateGUID(t *testing.T) {
 	setupTestDB(t)