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.

tests/ui/COVERAGE.md

@@ -28,7 +28,7 @@ Gate: every line below executes for BOTH personas unless marked
 | 21 | Podcasts: cross-user invisibility — own feed only (RLS §20 surfaces) | 🔲 | 🔲 |
 | 22 | Podcasts: order selector re-renders episode list; serial suggestion shown only for serial/audiobook feeds | 🔲 | 🔲 |
 | 23 | Podcasts: audio reader "Ep N/M" + prev/next episode; chain-advance to next episode | 🔲 | 🔲 |
-| 24 | Devices: Pair a Device — code lookup renders templ confirm card, claim binds + page refresh; wrong/expired code renders inline error partial (not a toast-only path) | 🔲 | 🔲 (registration invisible by design) |
+| 24 | Devices: Add New Device modal — pairing-code lookup renders templ confirm card in the modal, claim binds + page refresh; wrong/expired code renders inline error partial (not a toast-only path) | 🔲 | 🔲 (registration invisible by design) |
 
 ### Podcast-specific sweep notes (plan task 1.10)