Render one chapter format, not "Ch Chapter 250"

The userscript writes last_chapter/latest_chapter as "Chapter N" and the
poller writes the same label, so the templates' own "Ch " prefix doubled it on
every real row. A manual edit through the web UI stores a bare "250", so the
list carried two formats at once and stopped being scannable.

Move the formatting out of the templates into DisplayChapter/DisplayLatest on
Bookmark, which strip a leading "Chapter"/"Ch." lead-in and re-add exactly one
"Ch ", falling back to the numeric column when the label is empty.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/store.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"regexp"
+	"strconv"
 	"strings"
 
 	_ "modernc.org/sqlite"
@@ -41,6 +42,41 @@ func (b Bookmark) HasNewChapter() bool {
 	return b.LatestChapterNum != nil && *b.LatestChapterNum > b.LastChapterNum
 }
 
+// chapterLeadIn matches the prefix the userscript and the poller both write
+// ("Chapter 250"), so the UI can add exactly one "Ch " of its own instead of
+// doubling it. A manual edit through the web UI stores a bare "250", which is
+// the same string minus the lead-in.
+var chapterLeadIn = regexp.MustCompile(`(?i)^\s*(?:chapter|ch\.?)\s*`)
+
+func displayChapter(raw string, num float64) string {
+	rest := strings.TrimSpace(chapterLeadIn.ReplaceAllString(raw, ""))
+	if rest == "" {
+		rest = strconv.FormatFloat(num, 'f', -1, 64)
+	}
+	// "Ch " only makes sense in front of a number; anything else is a label the
+	// site gave us, so pass it through as written.
+	if rest[0] < '0' || rest[0] > '9' {
+		return rest
+	}
+	return "Ch " + rest
+}
+
+// DisplayChapter is the read-progress line: one canonical "Ch N" whatever
+// format the write came in as.
+func (b Bookmark) DisplayChapter() string {
+	return displayChapter(b.LastChapter, b.LastChapterNum)
+}
+
+// DisplayLatest is the same for the newest published chapter, which arrives
+// with the same "Chapter N" lead-in from both the userscript and the poller.
+func (b Bookmark) DisplayLatest() string {
+	var num float64
+	if b.LatestChapterNum != nil {
+		num = *b.LatestChapterNum
+	}
+	return displayChapter(b.LatestChapter, num)
+}
+
 // ContinueURL is where the Continue button points: the chapter last read, or
 // the series page when no chapter URL was ever captured.
 func (b Bookmark) ContinueURL() string {

backend/store_test.go

@@ -1034,3 +1034,41 @@ func TestOpenStoreMigratesAsuraHashlessCollision(t *testing.T) {
 		t.Fatalf("merge kept wrong row: %+v", merged)
 	}
 }
+
+func TestDisplayChapter(t *testing.T) {
+	cases := []struct {
+		name string
+		raw  string
+		num  float64
+		want string
+	}{
+		{"userscript label", "Chapter 250", 250, "Ch 250"},
+		{"abbreviated with dot", "Ch. 12", 12, "Ch 12"},
+		{"lowercase abbreviation", "ch 3", 3, "Ch 3"},
+		{"bare number from a manual edit", "45.5", 45.5, "Ch 45.5"},
+		{"empty falls back to the number", "", 7, "Ch 7"},
+		{"empty and zero", "", 0, "Ch 0"},
+		{"label with no number passes through", "Prologue", 0, "Prologue"},
+		{"title-like label keeps its words", "Chapter of the Sun", 0, "of the Sun"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := displayChapter(tc.raw, tc.num); got != tc.want {
+				t.Errorf("displayChapter(%q, %v) = %q, want %q", tc.raw, tc.num, got, tc.want)
+			}
+		})
+	}
+
+	b := Bookmark{LastChapter: "Chapter 9", LastChapterNum: 9}
+	if got := b.DisplayChapter(); got != "Ch 9" {
+		t.Errorf("DisplayChapter() = %q, want %q", got, "Ch 9")
+	}
+	if got := b.DisplayLatest(); got != "Ch 0" {
+		t.Errorf("DisplayLatest() with nothing captured = %q, want %q", got, "Ch 0")
+	}
+	num := 11.0
+	b.LatestChapter, b.LatestChapterNum = "Chapter 11", &num
+	if got := b.DisplayLatest(); got != "Ch 11" {
+		t.Errorf("DisplayLatest() = %q, want %q", got, "Ch 11")
+	}
+}

backend/templates/app.html

@@ -75,7 +75,7 @@
           {{else if .Favorite}}<span class="foot-rule brass"></span>{{end}}
         </span>
         <span class="recent-title">{{.Title}}</span>
-        <span class="recent-chapter">Ch {{.LastChapter}}{{if .HasNewChapter}} · New{{end}}</span>
+        <span class="recent-chapter">{{.DisplayChapter}}{{if .HasNewChapter}} · New{{end}}</span>
       </a>
       {{end}}
     </div>

backend/templates/card.html

@@ -21,10 +21,10 @@
       <p class="meta">
         <span class="site-{{.Site}}">{{.Site}}</span>
         <span class="sep">/</span>
-        <span class="chapter">Ch {{.LastChapter}}</span>
+        <span class="chapter">{{.DisplayChapter}}</span>
         {{if and (eq .Status "reading") .HasNewChapter}}
         <span class="sep">/</span>
-        <span class="new-chapter">Ch {{.LatestChapter}} out</span>
+        <span class="new-chapter">{{.DisplayLatest}} out</span>
         {{end}}
         {{if eq .Status "archived"}}
         <span class="sep">/</span>
@@ -86,7 +86,7 @@
         hx-post="/ui/bookmarks/{{.Key}}/chapter"
         hx-target="[id='card-{{.Key}}']" hx-swap="outerHTML"
         hx-indicator="[id='card-{{.Key}}']" hx-disabled-elt="input, button">
-    {{if .LatestChapter}}<p class="hint">Latest known: Ch {{.LatestChapter}}</p>{{end}}
+    {{if .LatestChapter}}<p class="hint">Latest known: {{.DisplayLatest}}</p>{{end}}
     <div class="field">
       {{/* max is a fat-finger guard, not a real ceiling — no series is near it. */}}
       <input name="chapter" type="number" step="0.1" min="0" max="9999"