ci: eliminate remote-cache download round-trips on the self-hosted runner (DT-KV-018)

See DT-KV-018 in kv-meta (PR #19) for the measured evidence.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/push.yml

@@ -35,6 +35,9 @@ jobs:
       - uses: actions/setup-go@40f1582b2485089dde7abd97c1529aa768e1baff # v5.6.0
         with:
           go-version: stable
+          # DT-KV-018: remote actions-cache round-trip (~287MB) vs the
+          # persistent runner-local GOMODCACHE — disable, don't fetch it.
+          cache: false
 
       - name: go build ./...
         run: go build ./...