feat(devices): pair-a-device card replaces the pending registration list

The Devices page's Pending Device Registrations section (Approve/Reject
cards broadcast to every account) is replaced by an always-visible Pair
a Device field: type the 6-digit code shown on the registering e-reader,
a templ-rendered confirm card shows what will be bound, and confirming
claims the device to the signed-in account.

Rendering ownership (AGENTS.md): the confirm card and every lookup
outcome are templ partials (PairingLookupResult) swapped by htmx from a
new SSR route POST /devices/pairing/lookup — the server decides what UI
looks like, no JSON-built HTML. Errors render as content because htmx
only swaps 2xx bodies (the route is web-only; the JSON API keeps real
status codes), and one delegated htmx:responseError listener in
device-management.ts toasts the non-swap failure path.

The claim confirm button posts straight to /api/devices/claim; success
comes back as HX-Refresh (same pattern as token regeneration), so the
page reloads into the paired state. No new TS module is needed — plain
htmx attributes drive the whole flow.

Ride-alongs: the Add New Device modal loses the device-type select and
the kobo manual form (its post-register UX depended on the broadcast
list and silently produced an unclaimable registration; native Kobo
sync is still server-side-only and will get its own pairing UX when it
lands) — the modal is now a single Connect-a-KOReader-Device guide with
the pairing steps. PendingRegistrationData, convertPending, and the
pending plumbing in the page handler are gone with the section.
ui-controls.md glossary and tests/ui COVERAGE.md updated in the same
commit as the control rename, per the drift gates.

internal/router/frontend.go

@@ -1152,7 +1152,6 @@ func registerFrontendRoutes(cfg *Config) {
 
 		var errorMsg string
 		var devices []handlers.DeviceInfo
-		var pendingList []templates.PendingRegistrationData
 
 		devices, err = cfg.DeviceHandler.GetDevicesData(c)
 		if err != nil {
@@ -1161,22 +1160,40 @@ func registerFrontendRoutes(cfg *Config) {
 			errorMsg = "Error loading devices"
 		}
 
-		pendingMaps, err := cfg.DeviceHandler.GetPendingRegistrationsData(c)
-		if err != nil {
-			log.Printf("GetPendingRegistrationsData failed: %v", err)
-			pendingList = []templates.PendingRegistrationData{}
-			if errorMsg == "" {
-				errorMsg = "Error loading pending registrations"
-			}
-		} else {
-			pendingList = convertPending(pendingMaps)
-		}
-
 		// Get base URL from database config with fallback to config/env var
 		baseURL := cfg.getBaseURL(c.Request().Context())
 
 		var buf bytes.Buffer
-		err = templates.Devices(user, devices, pendingList, errorMsg, baseURL).Render(c.Request().Context(), &buf)
+		err = templates.Devices(user, devices, errorMsg, baseURL).Render(c.Request().Context(), &buf)
+		if err != nil {
+			return err
+		}
+		return c.HTML(http.StatusOK, buf.String())
+	})
+
+	// Pairing-code lookup partial: renders the confirm card (or the
+	// reason nothing matched) into #pairing-lookup-result. Errors render
+	// as content — htmx only swaps 2xx bodies, and the pairing section is
+	// a web-only surface (the JSON API route keeps real status codes).
+	frontendProtected.POST("/devices/pairing/lookup", func(c *echo.Context) error {
+		userID, ok := c.Get("user_id").(string)
+		if !ok {
+			return c.HTML(http.StatusUnauthorized, "")
+		}
+
+		status := "found"
+		var deviceName, deviceType, pairingCode string
+		registration, err := handlers.ResolvePairingCode(userID, c.RealIP(), c.FormValue("pairing_code"))
+		if err != nil {
+			status = handlers.PairingErrorStatus(err)
+		} else {
+			deviceName = registration.DeviceName
+			deviceType = registration.DeviceType
+			pairingCode = registration.PairingCode
+		}
+
+		var buf bytes.Buffer
+		err = templates.PairingLookupResult(deviceName, deviceType, pairingCode, status).Render(c.Request().Context(), &buf)
 		if err != nil {
 			return err
 		}
@@ -1834,7 +1851,6 @@ func registerFrontendRoutes(cfg *Config) {
 		}
 		var errorMsg string
 		var devices []handlers.DeviceInfo
-		var pendingList []templates.PendingRegistrationData
 
 		devices, err = cfg.DeviceHandler.GetDevicesData(c)
 		if err != nil {
@@ -1843,22 +1859,11 @@ func registerFrontendRoutes(cfg *Config) {
 			errorMsg = "Error loading devices"
 		}
 
-		pendingMaps, err := cfg.DeviceHandler.GetPendingRegistrationsData(c)
-		if err != nil {
-			log.Printf("GetPendingRegistrationsData failed: %v", err)
-			pendingList = []templates.PendingRegistrationData{}
-			if errorMsg == "" {
-				errorMsg = "Error loading pending registrations"
-			}
-		} else {
-			pendingList = convertPending(pendingMaps)
-		}
-
 		// Get base URL from database config with fallback to config/env var
 		baseURL := cfg.getBaseURL(c.Request().Context())
 
 		var buf bytes.Buffer
-		err = templates.Devices(user, devices, pendingList, errorMsg, baseURL).Render(c.Request().Context(), &buf)
+		err = templates.Devices(user, devices, errorMsg, baseURL).Render(c.Request().Context(), &buf)
 		if err != nil {
 			return err
 		}