fix: target master (not GitHub default branch) in Nova Base sync PRs

sync-nova-base.yml checked out and PR'd against whatever branch GitHub
considers the repo default - which is 'main', a read-only mirror kept in
sync FROM master (auto-pr.yml/auto-merge.yml only flow master -> main,
never the reverse). master is what the live app actually fetches configs
from (see wallet-android's CHAINS_URL etc. all pointing at .../master/...).

Net effect: every one of the 29 accumulated 'Sync from Nova Base' PRs
(#1 through #36, 2026-02-09 through 2026-07-09) landed on a branch nothing
downstream ever reads, so 5 months of upstream Nova chain/RPC/asset
maintenance never reached production regardless of whether those PRs got
merged. Explicit ref/base: master makes future runs target the branch that
actually matters; the 29 stale main-targeted PRs are being closed as
superseded now that #36's content has been applied to master directly (see
next commit).

.github/workflows/sync-nova-base.yml

@@ -25,6 +25,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
         with:
+          ref: master
           submodules: recursive
           fetch-depth: 0
           token: ${{ secrets.GITHUB_TOKEN }}
@@ -94,6 +95,7 @@ jobs:
             ---
             *This PR was automatically created by the sync workflow.*
           branch: sync/nova-base-${{ env.NOVA_COMMIT }}
+          base: master
           delete-branch: true
           labels: |
             automated