Add a timeline page grouping photos by day

New /timeline/ page renders photos grouped into consecutive same-day
runs (ISO date heading plus per-day count), reusing the square grid.
groupByDay collapses the newest-first photo list; the page is not
paginated. Linked from the profile header.

generator.go

@@ -43,6 +43,14 @@ type Photo struct {
 	Date    time.Time
 }
 
+// DayGroup is a run of photos sharing the same calendar day, for the timeline.
+type DayGroup struct {
+	day    string // "2006-01-02", grouping key (unexported: not for templates)
+	Label  string // "14 June 2026"
+	Count  int
+	Photos []Photo
+}
+
 type Generator struct {
 	contentDir  string
 	outputDir   string
@@ -120,6 +128,9 @@ func (g *Generator) Build() error {
 			return err
 		}
 	}
+	if err := g.renderTimeline(photos); err != nil {
+		return err
+	}
 	if err := g.renderFeed(photos); err != nil {
 		return err
 	}
@@ -385,6 +396,48 @@ func (g *Generator) renderPhotoPage(p Photo, newer, older *Photo) error {
 	})
 }
 
+// groupByDay collapses photos (already sorted newest first) into per-day runs,
+// preserving order. Two photos land in the same group iff their dates share a
+// calendar day.
+func groupByDay(photos []Photo) []DayGroup {
+	var groups []DayGroup
+	for _, p := range photos {
+		day := p.Date.Format("2006-01-02")
+		if n := len(groups); n > 0 && groups[n-1].day == day {
+			groups[n-1].Photos = append(groups[n-1].Photos, p)
+			groups[n-1].Count++
+			continue
+		}
+		groups = append(groups, DayGroup{
+			day:    day,
+			Label:  day, // ISO 2006-01-02
+			Count:  1,
+			Photos: []Photo{p},
+		})
+	}
+	return groups
+}
+
+// renderTimeline writes public/timeline/index.html, photos grouped by day.
+func (g *Generator) renderTimeline(photos []Photo) error {
+	dir := filepath.Join(g.outputDir, "timeline")
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return err
+	}
+	return g.render("timeline.html", filepath.Join(dir, "index.html"), map[string]any{
+		"Groups":      groupByDay(photos),
+		"Total":       len(photos),
+		"BaseURL":     g.baseURL,
+		"Year":        time.Now().Year(),
+		"Author":      g.author,
+		"Handle":      g.handle,
+		"Initial":     g.initial(),
+		"FontsURL":    g.fontsURL,
+		"SerifFamily": g.serifFamily,
+		"MlFamily":    g.mlFamily,
+	})
+}
+
 func (g *Generator) render(tmpl, dst string, data any) error {
 	f, err := os.Create(dst)
 	if err != nil {