fix(backlog): item #320 used a status glyph the invariant does not allow

BACKLOG #320 was filed with `> 📋 **Filed 2026-08-01, not started.**`. The
status gate accepts five glyphs — ✅ SHIPPED, ⛔ DECLINED, 🪦 RETIRED (closed),
🔢 prioritized, 🚧 in progress (open) — and 📋 is not among them, so the item
read as declaring no status at all.

That turned main red at 13:26 (run 30701716567, both the ubuntu and windows-2022
legs) and every PR opened since inherits it through the merge ref, including this
one. The item is open and not started, so 🚧 is the correct glyph; the wording is
unchanged and it still carries exactly one banner.

Author: wshallwshall

docs/BACKLOG.md

@@ -7298,7 +7298,7 @@ So `calling_ae_allowlist` **alone** satisfies a gate whose stated purpose is to
 
 ## 320. windows-2025 MLLP ingress is ~10x slower than a healthy runner
 
-> 📋 **Filed 2026-08-01, not started.** Diagnosis only — the CI symptom is already fixed (#115, `06fd327d`) by widening the reconcile's stranding budget. This item is the **underlying capacity fact**, which that fix does not address and deliberately did not try to.
+> 🚧 **Filed 2026-08-01, not started.** Diagnosis only — the CI symptom is already fixed (#115, `06fd327d`) by widening the reconcile's stranding budget. This item is the **underlying capacity fact**, which that fix does not address and deliberately did not try to.
 
 **Type:** CI/runner capacity — not a correctness defect. No message was ever lost in any observed instance.