feat: add Zotero 10 support

Bump strict_max_version to 10.0.* and esbuild target to firefox140
(Zotero 9/10 Firefox 140 ESR base). Update docs accordingly.

AGENTS.md

@@ -25,7 +25,7 @@ npm run release           # Bump version, commit, tag, and build
 This project does not currently have automated tests. To test manually:
 
 1. Run `npm run build` to create the XPI
-2. Install the XPI in Zotero 7
+2. Install the XPI in Zotero 7–10
 3. Test export functionality manually via Tools menu
 
 ---