Fix CI: add missing Remotes for ccflowR + presto (dependency-resolution failure)

[Huangy57]

Problem

R-CMD-check (all 7 platform/version jobs) and lint have been failing on
main — since the package was first set up — at the "Setup R dependencies"
step, before any checking runs:

! Could not solve package dependencies:
  * Can't install dependency ccflowR
  * Can't install dependency presto
  * ccflowR: Can't find package called ccflowR, presto.

DESCRIPTION declares ccflowR and presto under Suggests:, but Remotes:
only listed nichenetr and multinichenetr. Both ccflowR and presto are
GitHub-only (not on CRAN/Bioconductor), so pak can't resolve them and the
dependency solve aborts — taking down R-CMD-check and lint together.

This is independent of the tutorials work in #2; it fails on a clean main.

Fix

Add the two missing remotes, using the same sources/pins already in
inst/bootstrap.R and the install docs:

Remotes:
    saeyslab/nichenetr,
    saeyslab/multinichenetr,
    immunogenomics/presto,
    settylab/ccflowR@6056c0fe1d1cecfc68aa059bacfbe6bd16725231

• presto → immunogenomics/presto (public) — resolves with CI's default
  token.
• ccflowR → settylab/ccflowR at the audited commit
  6056c0fe1d1cecfc68aa059bacfbe6bd16725231 (the SHA pinned in
  inst/bootstrap.R).

⚠️ Remaining CI step — needs a maintainer action (private repo)

settylab/ccflowR is a private repository. The CI workflow
(.github/workflows/R-CMD-check.yaml) authenticates setup-r-dependencies with
the default GITHUB_TOKEN, which can only read this repo — not other private
repos in the org. So with this PR alone, pak will get past presto but still
fail to clone the private ccflowR, and CI will stay red.

To fully green CI, one of:

1. Give CI a PAT with read access to settylab/ccflowR (recommended). Create
   a repo/org secret (e.g. CCFLOWR_PAT) holding a PAT (classic repo scope, or
   a fine-grained token with read access to settylab/ccflowR), then pass it to
   each setup-r-dependencies step:

   - name: Setup R dependencies
     uses: r-lib/actions/setup-r-dependencies@v2
     with:
       extra-packages: any::rcmdcheck
       needs: check
       github-token: ${{ secrets.CCFLOWR_PAT }}

   (and likewise for the lint and test-coverage jobs). I did not add this
   because it depends on a secret only a maintainer can create; happy to push the
   workflow edit once the secret name is decided.

2. Or stop CI from installing the private optional dep — e.g. set
   dependencies: '"hard"' on the setup-r-dependencies steps so only
   Imports/Depends are installed. This greens CI without a PAT but skips all
   Suggests-based example/test coverage (Seurat, nichenetr, …), so it's a
   coverage tradeoff worth a maintainer's call.

Verification

After this change, CI dependency resolution should no longer complain about
presto; the remaining failure (if the PAT secret isn't yet configured) will be
on cloning the private ccflowR, confirming the isolation above. Posting the
check results in a comment.