Remove broken autofix-bot marketplace entry

[dicksontsai]

Summary

Removes the autofix-bot entry from .claude-plugin/marketplace.json — its source points to ./external_plugins/autofix-bot, which has never existed in this repository.

Background

• The entry was added in updates(staging): merge staging additions into main #677 (staging merge) without the corresponding plugin directory
• Git history shows no commits ever touched external_plugins/autofix-bot/
• The homepage URL points to claude-plugins-public (different repo), suggesting the entry was copied over but the plugin files were not

Verification

Checked all local string-path sources in marketplace.json — this was the only broken one:

jq -r '.plugins[] | select(.source | type == "string") | .source' .claude-plugin/marketplace.json | \
  while read -r path; do [ ! -d "${path#./}" ] && echo "MISSING: $path"; done

(Entries with object-typed source — remote URLs, git-subdir — are not affected by this check.)