feat(ci): repo-branch/repo-commit inputs for cross-repo builds

github.ref_name/github.sha refer to the workflow's own repo. When
repo-url points elsewhere (build-nsInnoUnp builds
nsis-plugin-nsinnounp) the workflow's branch does not exist there
("Remote branch ... not found in upstream origin"). New inputs:
- repo-branch: target branch (default: github.ref_name)
- repo-commit: target commit (default: github.sha only if repo-url
  not overridden; cross-repo => empty = branch tip, no pin)
build-nsInnoUnp.yml sets repo-branch: main.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/build-nsInnoUnp.yml

@@ -37,6 +37,9 @@ jobs:
           # host-side clone + zip transfer transport.
           use-git-clone:   'false'
           repo-url:        'ssh://gitea-ci/Simone/nsis-plugin-nsinnounp.git'
+          # Cross-repo build: github.ref_name is this repo's branch, not
+          # nsis-plugin-nsinnounp's. Pin the target repo's branch.
+          repo-branch:     'main'
           # Suffix disambiguates artifact dirs: F:\CI\Artifacts\{run_id}-{attempt}-windows
           job-id-suffix:   '${{ matrix.target }}'
           artifact-name:   'nsis-plugin-nsinnounp-${{ matrix.target }}-${{ github.ref_name }}'