feat: add source-dir and repo-url inputs for external repo support

Allow changelog generation from upstream repositories instead of only
the current working directory. Supports packaging repos that contain
only rpm spec files while the source lives in an external git repo.

- source-dir: point at an existing local checkout
- repo-url: action clones a bare copy automatically
- source-dir takes precedence if both are set

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

action.yml

@@ -44,6 +44,22 @@ inputs:
     default: |
       ^- chore: bump version
       ^- Merge
+  source-dir:
+    description: >
+      Path to a local git checkout to collect commits from, instead
+      of the current working directory. Useful when your packaging
+      repo is separate from the upstream source repo and you have
+      already cloned the source elsewhere in the workflow.
+    required: false
+    default: ''
+  repo-url:
+    description: >
+      URL of an external git repository to collect commits from.
+      The action will clone (bare, tags-only) this repo into a
+      temporary directory and read its history. Mutually exclusive
+      with source-dir — if both are set, source-dir wins.
+    required: false
+    default: ''
 
 runs:
   using: composite
@@ -57,6 +73,8 @@ runs:
         CHANGELOG_AUTHOR: ${{ inputs.author }}
         TAG_PATTERN: ${{ inputs.tag-pattern }}
         EXCLUDE_PATTERNS: ${{ inputs.exclude-patterns }}
+        SOURCE_DIR: ${{ inputs.source-dir }}
+        REPO_URL: ${{ inputs.repo-url }}
       run: |
         bash "${{ github.action_path }}/scripts/generate-rpm-changelog.sh" \
           "$SPEC" "$VERSION"