fix(bug-fix): set add-labels max to 1 consistently across source and lock

A prior autofix flipped the authored frontmatter add-labels.max back to 2,
re-introducing the mismatch: source said 2, the compiled lock enforced 1, and
Step 8 prose says 'exactly one status label per run'. The workflow only ever
applies a single status label per run (needs-assessment | needs-reproduction |
fix-proposed | fix-blocked), so 1 is the correct, tightest contract and matches
the compiled lock. Set the frontmatter to max:1 so source, lock, and prose all
agree (also avoids the lock staleness guard failing on a frontmatter mismatch).

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Author: BenBtg

.github/workflows/bug-fix.md

@@ -37,7 +37,7 @@ safe-outputs:
     max: 1
   add-labels:
     allowed: [needs-assessment, needs-reproduction, fix-proposed, fix-blocked]
-    max: 2
+    max: 1
 ---
 
 # Fix Bug from Labeled Issue