Fix XPI download failure when release tag contains slashes

Tags like "zotero-plugin/v0.9.0" contain "/" which broke the download
filename path construction, causing the file write to target a
non-existent subdirectory.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/zotero_scraper/services/cache_builder.py

@@ -294,7 +294,8 @@ class ReleaseCacheBuilder:
 
         # Download XPI
         owner, name = repo.split("/")
-        filename = f"{owner}#{name}+{tag}@{xpi_id}.xpi"
+        safe_tag = tag.replace("/", "_")
+        filename = f"{owner}#{name}+{safe_tag}@{xpi_id}.xpi"
         xpi_path = self.downloader.download(xpi_url, filename)
 
         if not xpi_path:

src/zotero_scraper/services/scraper.py

@@ -190,8 +190,9 @@ class AddonScraper:
         release.releaseDate = xpi_asset.updated_at
 
         # Download and parse XPI
+        safe_tag = release.tagName.replace("/", "_")
         xpi_filename = (
-            f"{plugin.owner}#{plugin.repository}+{release.tagName}@{xpi_asset.id}.xpi"
+            f"{plugin.owner}#{plugin.repository}+{safe_tag}@{xpi_asset.id}.xpi"
         )
 
         # Determine priority sources based on Zotero version