fix(devices): pairing input moves into the Add Device modal

The pairing field sat at the bottom of the Devices page, below the
device grid — unreachable on any account with more than a screenful of
devices (the user's dev account has ~480 accumulated test devices;
scrolling 224k px to reach the field is a non-starter). The Add Device
button at the top of the page is where pairing intent already lives,
so the code input and Find device button now sit inside the Connect a
KOReader Device modal as instruction step 6, with the confirm card
swapping into the same modal (container keeps the pairing-lookup ids;
the htmx error-toast listener scopes to #add-device-modal now).

Verified live: modal renders the full instruction list + input, a
wrong code swaps the templ error partial inside the modal, and claim
still HX-Refreshes on success (modal state resets with the reload,
paired device appears in the grid).

ui-controls glossary where-fields and the COVERAGE row updated with
the control's new home.

web/src/device-management.ts

@@ -463,13 +463,13 @@ function setupEventDelegation(): void {
     }
   });
 
-  // Pairing section: htmx only swaps 2xx bodies, so claim/lookup failures
-  // (wrong code, rate limit, expired) would otherwise fail silently.
-  // Content-level answers come from the templ partial; this toast covers
-  // the non-swap error path.
+  // Pairing (Add Device modal): htmx only swaps 2xx bodies, so claim/lookup
+  // failures (wrong code, rate limit, expired) would otherwise fail
+  // silently. Content-level answers come from the templ partial; this
+  // toast covers the non-swap error path.
   document.body.addEventListener("htmx:responseError", (e) => {
     const detail = (e as CustomEvent<{ requestConfig?: { elt?: Element } }>).detail;
-    if (detail?.requestConfig?.elt?.closest("#pairing-section")) {
+    if (detail?.requestConfig?.elt?.closest("#add-device-modal")) {
       showToast("Pairing failed — check the code and try again.", "error");
     }
   });