book3: add Athel Repository to kingdom-of-corvel map and registry

- Proximity map: Thorngate box now shows Athel Repository (E coast)
- Location Registry: new row with site summary and pointer to
  the future athel-repository.md detail file

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

world/locations/kingdom-of-corvel.md

@@ -48,7 +48,10 @@ No counts. Corvel does not use the title.
          │   ║   ALDERMERE    ║════════║    THORNGATE    ║ │
          │   ║   (Duke Holven)║ peers  ║ (Duchess Pamira)║ │
          │   ║   ★ Aldermere  ║        ║   ★ Thorngate   ║ │
-         │   ╚═══════╤════════╝        ╚════════╤════════╝ │
+         │   ╚═══════╤════════╝        ║  • Athel        ║ │
+         │           │                 ║    Repository   ║ │
+         │           │                 ║    (E coast)    ║ │
+         │           │                 ╚════════╤════════╝ │
          │           │                          │           │
          │     ╔═════╧══════════════════════════╧═════╗    │
          │     ║         THE CROWNHOLD                 ║    │
@@ -112,6 +115,7 @@ Every named place established in Books 1 and 2, plus the new duchy seats introdu
 |---|---|---|---|---|
 | **Drenwick** | City (river junction) | Sudermere | Book 1 Ch01 | Phelan's home base. Guild-dominated. Multiple districts. |
 | **Thorngate** | City | Thorngate | Book 1 Ch04 | Compact's northern regional office. Pamira's duchy seat. ~4 days N of Drenwick. |
+| **Athel Repository** | Pre-Compact ruin | Thorngate | Book 3 | 45-acre eastern-coastal site on Pamira's land. Walled pre-Compact research compound + three cliff-face mines. Sealed perimeter gate with adaptive ward. 6-level underground repository beneath the Descent Building. Dragon colony in Mine 1. Surveyed 20 years ago by Devod's Pathfinder team; opened by Phelan in Book 3. See `world/locations/athel-repository.md` (to be created during Book 3 drafting) for full site detail. |
 | **Caldburn** | Town | Sudermere | Book 1 Ch04 | Phelan's prior residence. Uneventful per guild background check. |
 | **Brenwick** | Town | Sudermere | Book 1 Ch12 | East of Drenwick. Former ghostveil moss site, acquired by Compact. |
 | **Henwick** | Rural / orchard | Sudermere | Book 2 Ch01 | Devod's delivery route source. East of Drenwick. |