Add copyright footer to gallery and photo pages

Renders a © 2000–<current-year> Ashik Salahudeen line under both the
index and each photo page. The year comes from time.Now().Year() at
render time so the range stays current without manual updates.

generator.go

@@ -274,6 +274,7 @@ func (g *Generator) renderIndex(photos []Photo) error {
 	return g.render("index.html", filepath.Join(g.outputDir, "index.html"), map[string]any{
 		"Photos":  photos,
 		"BaseURL": g.baseURL,
+		"Year":    time.Now().Year(),
 	})
 }
 
@@ -286,6 +287,7 @@ func (g *Generator) renderPhotoPage(p Photo) error {
 	return g.render("photo.html", filepath.Join(dir, "index.html"), map[string]any{
 		"Photo":   p,
 		"BaseURL": g.baseURL,
+		"Year":    time.Now().Year(),
 	})
 }