Rename series to 'AI Papers of the Week' and add 2025-2026 entries

- Rename the series from "ML Papers of the Week" to "AI Papers of the Week" across the README and SUMMARY
- Add all 2026 weekly issues (January through April 12, 2026) with TOC anchors and full entries
- Backfill missing 2025 weekly issues to keep the timeline contiguous
- Bold paper titles across every entry so formatting matches the December 2024 style (**Title** - description)

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

SUMMARY.md

@@ -1,5 +1,5 @@
 # Table of contents
 
-* [ML Papers of The Week](README.md)
+* [AI Papers of the Week](README.md)
 * [pics](pics/README.md)
 * [Research](research/README.md)