Toggle tasks and edit view settings via htmx

Task checkboxes post themselves (hx-post="?toggle=N") and flip back when
the save fails, replacing tasks.js. View settings are a server-rendered
form dialog with real radios and a select, replacing view-settings.js;
with that, postReplace has no callers left.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

render.go

@@ -58,8 +58,6 @@ type pageData struct {
 	Content        template.HTML
 	Entries        []entry
 	View           string // listing view style: "list" or "thumbnail"
-	Sort           string // listing sort key: "name" / "modified" / "size"
-	Order          string // listing sort order: "asc" / "desc"
 	SpecialContent template.HTML
 	SidebarWidget  template.HTML
 	SuppressTOC    bool