refactor: use reusable bump-upstream workflow [skip ci]

chore: bump openclaw to 2026.6.11

Splits the build-hash logic into a thin caller for the new
`dappnode/workflows/.github/workflows/dappnode-build-hash.yml@master`
reusable workflow. `build.yml` (new) now handles both push and
workflow_dispatch; `main.yml` is reduced to the release job only.

Also upgrades `actions/checkout` to v7 and Node 24 (with
`actions/setup-node@v6`) for the release job.

The reusable workflow auto-detects the event: on push to a non-default
branch it builds, pins to Pinata, and posts a comment authored by
tropibot[bot] on the PR; on push to the default branch it does a
test build only. (The previous `if: github.event_name == 'push'
&& github.ref != 'refs/heads/main'` guard is no longer needed
because the SDK already handles that case.)

The release job used a broad `on.push` (no branch filter) plus an
`if:` condition that checked `github.ref == 'refs/heads/<default>'`.
This worked but was verbose and easy to get wrong (tailscale had
`refs/heads/main` instead of `refs/heads/master`).

Simplify: filter in the trigger itself, drop the `if` condition.
Same behavior, half the YAML. Also adds `workflow_dispatch` so the
release can be triggered manually.

ci: use dappnode-build-hash reusable workflow

`build.yml` triggers on `push` and `workflow_dispatch`. The reusable
`dappnode-build-hash.yml` SDK already auto-detects pushes to the default
branch and runs a no-op test build (no IPFS pin, no comment), so the
workflow run is wasted CI on every merge.

Add `branches-ignore: ["main"]` to the push trigger so the workflow
doesn't even start on default-branch pushes. `workflow_dispatch` and
pushes to other branches (e.g. tropibot bump branches) still trigger it
as before.

ci: skip build.yml on default branch pushes

* chore: bump openclaw upstream to 2026.7.1

* chore: set UPSTREAM_VERSION to 2026.7.1

* fix: address OpenClaw runtime warnings

* fix + feat: Fix config and add nexus login

---------

Co-authored-by: tropibot[bot] <285933081+tropibot[bot]@users.noreply.github.com>
Co-authored-by: hcastc00 <hcastc00@estudiantes.unileon.es>