feat(manage): add /manage pages to edit and delete photos, behind -manage

/manage lists every photo; /manage/edit/{slug} rewrites the photo's
.toml sidecar (caption, date), /manage/delete/{slug} asks for
confirmation and then removes the image, its sidecar and everything
generated from them. Builds now drop day pages of days without photos
and pager pages past the last one, so a delete or a date change leaves
nothing behind.

The pages are off by default: the routes are only registered with
-manage, so an install that does not opt in has no such code path and
answers 404. NixOS gets services.photogallery.manage.enable, which
also adds the nginx location only when on. Like /upload, the pages
carry no auth of their own and are not linked from the public site.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

main.go

@@ -20,6 +20,7 @@ func main() {
 	serifFamily := flag.String("serif-family", "Crimson Pro", "CSS font-family for the primary serif text")
 	mlFamily    := flag.String("ml-family", "Manjari", "CSS font-family for the alt-script (Malayalam) bio line")
 	pageSize    := flag.Int("page-size", 60, "photos per page on the timeline and grid views (timeline packs whole days, so pages vary slightly around this)")
+	manage      := flag.Bool("manage", false, "serve the /manage pages for editing and deleting published photos (off by default; put them behind auth in nginx)")
 	defaultView := flag.String("default-view", viewTimeline, "view published at the site root: \"timeline\" or \"grid\"; the other one is published under /<name>/")
 	flag.Parse()
 
@@ -46,6 +47,6 @@ func main() {
 	defer w.Close()
 	go w.Watch()
 
-	s := NewServer(*port, *contentDir, *outputDir, *serve, g)
+	s := NewServer(*port, *contentDir, *outputDir, *serve, *manage, g)
 	log.Fatal(s.Listen())
 }