fix(content): refresh stale Wikipedia ZIM catalog URLs

The Wikipedia download catalog pinned dated Kiwix filenames from 2025-12.
Kiwix rotates ZIMs by date and removes old ones, so wikipedia_en_all_mini_2025-12.zim
now 404s on download (reported in #1015). Refreshed every variant to the newest
file Kiwix currently serves and corrected sizes:

- top-mini:  2025-12 -> 2026-06 (313 -> 316 MB)
- top-nopic: 2025-12 -> 2026-06 (2100 -> 2136 MB)
- all-mini:  2025-12 -> 2026-06 (11400 -> 11951 MB)  [the 404 case]
- all-nopic: 2025-12 -> 2026-03 (49000 -> 49521 MB)
- all-maxi:  2026-02 (already current)

All five URLs verified live (HTTP 200). This is a manual refresh; the
underlying staleness (static dated URLs that age out) is tracked separately
for a structural fix that resolves URLs from the live Kiwix catalog at
download time.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

collections/wikipedia.json

@@ -1,5 +1,5 @@
 {
-  "spec_version": "2026-03-23",
+  "spec_version": "2026-06-24",
   "options": [
     {
       "id": "none",
@@ -13,33 +13,33 @@
       "id": "top-mini",
       "name": "Quick Reference",
       "description": "Top 100,000 articles with minimal images. Great for quick lookups.",
-      "size_mb": 313,
-      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_top_mini_2025-12.zim",
-      "version": "2025-12"
+      "size_mb": 316,
+      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_top_mini_2026-06.zim",
+      "version": "2026-06"
     },
     {
       "id": "top-nopic",
       "name": "Popular Articles",
       "description": "Top articles without images. Good balance of content and size.",
-      "size_mb": 2100,
-      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_top_nopic_2025-12.zim",
-      "version": "2025-12"
+      "size_mb": 2136,
+      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_top_nopic_2026-06.zim",
+      "version": "2026-06"
     },
     {
       "id": "all-mini",
       "name": "Complete Wikipedia (Compact)",
       "description": "All 6+ million articles in condensed format.",
-      "size_mb": 11400,
-      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_all_mini_2025-12.zim",
-      "version": "2025-12"
+      "size_mb": 11951,
+      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_all_mini_2026-06.zim",
+      "version": "2026-06"
     },
     {
       "id": "all-nopic",
       "name": "Complete Wikipedia (No Images)",
       "description": "All articles without images. Comprehensive offline reference.",
-      "size_mb": 49000,
-      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_all_nopic_2025-12.zim",
-      "version": "2025-12"
+      "size_mb": 49521,
+      "url": "https://download.kiwix.org/zim/wikipedia/wikipedia_en_all_nopic_2026-03.zim",
+      "version": "2026-03"
     },
     {
       "id": "all-maxi",