chore(gadfly): bump reusable pin to 0d51879 (opencode-capable image)

Picks up gadfly's opencode/<model> engine — the reusable at this ref pins the
sha-bb98fae reviewer image that bundles the OpenCode CLI. Also correct the pin
comment: this is an immutable sha pin, not the v1 tag it claimed to track.

.gitea/workflows/adversarial-review.yml

@@ -38,10 +38,11 @@ jobs:
           && (github.actor == 'steve'
               || github.actor == 'fizi'
               || github.actor == 'dazed'))
-    # Tracks gadfly's v1 release tag — a curated pointer re-moved on each release
-    # (unlike @main, which moves on every push). Central swarm tuning propagates
-    # here automatically; the tradeoff vs a full sha pin is that v1 is mutable.
-    uses: steve/gadfly/.gitea/workflows/review-reusable.yml@8eb0265e759e8c37ade8eaa8cb4b3aa9c7a5a169
+    # Pinned to an immutable gadfly commit (not @v1): our act_runners are long-lived
+    # and cache the reusable-workflow ref, so a moved v1 tag keeps resolving to the
+    # stale cached copy. A unique sha forces a cache miss → fresh fetch. Bump this
+    # sha to adopt central swarm changes.
+    uses: steve/gadfly/.gitea/workflows/review-reusable.yml@0d518794507ab5fb349887679c931888c5ca2669
     # Least privilege: forward only the review secrets (not `secrets: inherit`,
     # which would expose every repo secret). GITEA_TOKEN is the automatic token.
     secrets: