docs(nav): Administration section lives in docs/admin/; sidebar ordered by usability

Two structural changes, one owner-approved plan:

- Move the admin guides out of docs/user/ into their own docs/admin/
  area — admin-guide.md becomes the Administration section landing page
  (pinned first), and the 32-line admin-library-management.md stub
  becomes admin/libraries.md, which the admin-docs build-out rebuilds
  into the real Libraries page next. Retired URLs 301 via a new
  docRedirects map in the docs HTTP handler (checked before .md
  canonicalization so even .md spellings one-hop to the new clean URL);
  the two inbound links (docs index, user-guide front door) updated.

- Sidebar direct items now sort by usabilityOrder — an explicit,
  per-section display order — instead of alphabetically: User Guide
  mirrors the 'Where to go' table on user-guide.md, Devices orders
  Android → KOReader → Kobo (alphabetically Kobo used to sort ahead of
  KOReader), and Administration pre-lists its planned pages so each
  lands in place as the admin build writes it. Unlisted docs fall back
  to alphabetical after the listed ones. Display-order only by
  construction: the URL-driven expand/highlight machinery keys on
  containsURL membership and never sees sort order — nav tests updated
  to pin the new orders plus a real-tree test
  (TestBuildNavigationUsabilityOrder) guarding all three sections.

internal/docs/navigation.go

@@ -28,6 +28,47 @@ var sectionOrder = []struct {
 	{Title: "Contributing", Icon: "heart"},
 }
 
+// usabilityOrder pins an explicit, usability-first display order for a
+// section's direct nav items, overriding the alphabetical fallback (owner
+// request 2026-11-02: order the menu by how people work, not by letter —
+// the User Guide list mirrors the "Where to go" table on user-guide.md).
+// Values are doc paths without the .md suffix; anything in the section not
+// listed sorts alphabetically AFTER the listed items. Display-only: the
+// open/highlight machinery keys on URL membership (containsURL) and is
+// order-blind, so URL-driven expansion is unaffected. Administration lists
+// its planned pages up front so each lands in place as it is written.
+var usabilityOrder = map[string][]string{
+	"User Guide": {
+		"user/dashboard",
+		"user/library-browsing",
+		"user/collections",
+		"user/searching-and-filtering",
+		"user/podcasts",
+		"user/reader-guide",
+		"user/themes",
+		"user/profile-guide",
+		"user/sync-guide",
+		"user/calibre-integration",
+	},
+	"Devices": {
+		"user/devices/android-app",
+		"user/devices/koreader-setup",
+		"user/devices/kobo-setup",
+	},
+	"Administration": {
+		"admin/admin-guide",
+		"admin/dashboard",
+		"admin/libraries",
+		"admin/library-processing-issues",
+		"admin/archived-items",
+		"admin/podcasts",
+		"admin/hash-conflicts",
+		"admin/users",
+		"admin/settings",
+		"admin/scanning",
+	},
+}
+
 // groupTitleOverrides fixes casing that naive title-casing gets wrong.
 var groupTitleOverrides = map[string]string{
 	"admin":     "Admin",
@@ -104,12 +145,16 @@ func placeDoc(docPath string) navPlacement {
 		if rest == "user-guide.md" {
 			return navPlacement{section: "User Guide", pin: -50}
 		}
-		// Admin-facing guides are their own top-level section too.
-		if strings.HasPrefix(rest, "admin-") {
-			return navPlacement{section: "Administration"}
-		}
 		return navPlacement{section: "User Guide"}
 
+	case strings.HasPrefix(docPath, "admin/"):
+		// Admin docs live in their own area (docs/admin/); the guide is
+		// the section landing page.
+		if docPath == "admin/admin-guide.md" {
+			return navPlacement{section: "Administration", pin: -50}
+		}
+		return navPlacement{section: "Administration"}
+
 	case strings.HasPrefix(docPath, "developer/api/"):
 		rest := strings.TrimPrefix(docPath, "developer/api/")
 		if dir, _, ok := strings.Cut(rest, "/"); ok {
@@ -256,14 +301,27 @@ func (h *DocsHandler) BuildNavigation(currentPath string) *templates.Navigation
 		build := builds[spec.Title]
 		section := templates.NavSection{Title: spec.Title, Icon: spec.Icon}
 
-		// Direct items: pinned landing pages lead, then alphabetical
-		// (case-insensitive — KOReader must not sort before Kobo).
+		// Direct items: pinned landing pages lead, then usability order
+		// (see usabilityOrder), then alphabetical among anything unlisted.
+		order := usabilityOrder[spec.Title]
+		rankOf := func(url string) int {
+			for i, p := range order {
+				if docURL(p) == url {
+					return i
+				}
+			}
+			return len(order)
+		}
 		items := append([]templates.NavItem(nil), build.items...)
 		sort.SliceStable(items, func(i, j int) bool {
 			pi, pj := build.pinned[items[i].URL], build.pinned[items[j].URL]
 			if pi != pj {
 				return pi
 			}
+			ri, rj := rankOf(items[i].URL), rankOf(items[j].URL)
+			if ri != rj {
+				return ri < rj
+			}
 			return strings.ToLower(items[i].Title) < strings.ToLower(items[j].Title)
 		})
 		section.Items = items