fix: arxiv year

docs/storage-layout.md

@@ -53,16 +53,21 @@ papers/arxiv/YEAR/arxiv-NORMALIZED_ID/
 ```
 
 Where:
-- `YEAR` is extracted from the arXiv ID (e.g., `2212.06340` → `2022`)
+- `YEAR` is extracted from the arXiv ID (e.g., `2212.06340` → `2022`, `0001.12345` → `2000`)
 - `NORMALIZED_ID` replaces dots and version numbers with underscores
   - `2212.06340` → `arxiv-2212_06340`
   - `2212.06340v2` → `arxiv-2212_06340v2`
 
+The year extraction follows arXiv's YYMM.NNNNN format:
+- Years 00-89 map to 2000-2089
+- Years 90-99 map to 1990-1999
+
 **Examples:**
 ```
-papers/arxiv/2022/arxiv-2212_06340/
-papers/arxiv/2023/arxiv-2301_12345v1/
-papers/arxiv/2024/arxiv-2405_98765/
+papers/arxiv/2022/arxiv-2212_06340/    # 2212.06340 -> year 2022
+papers/arxiv/2023/arxiv-2301_12345v1/  # 2301.12345v1 -> year 2023  
+papers/arxiv/2000/arxiv-0001_98765/    # 0001.98765 -> year 2000
+papers/arxiv/1999/arxiv-9912_12345/    # 9912.12345 -> year 1999
 ```
 
 ### Local Papers