feat: wire slop:diff into /review as advisory diagnostic

Adds Step 3.5 to the review template: runs bun run slop:diff against
the base branch to catch AI code quality issues (empty catches,
redundant return await, overcomplicated abstractions). Advisory only,
never blocking. Skips silently if slop-scan is not installed.

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

review/SKILL.md.tmpl

@@ -69,6 +69,19 @@ git fetch origin <base> --quiet
 
 Run `git diff origin/<base>` to get the full diff. This includes both committed and uncommitted changes against the latest base branch.
 
+## Step 3.5: Slop scan (advisory)
+
+Run a slop scan on changed files to catch AI code quality issues (empty catches,
+redundant `return await`, overcomplicated abstractions):
+
+```bash
+bun run slop:diff origin/<base> 2>/dev/null || true
+```
+
+If findings are reported, include them in the review output as an informational
+diagnostic. Slop findings are advisory, never blocking. If slop:diff is not
+available (e.g., slop-scan not installed), skip this step silently.
+
 ---
 
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