Enable add-comment for non-commentable events via PR resolution

[Copilot]

The safe-outputs.add-comment feature only worked for workflows triggered by commentable events (issues, PRs, discussions). Workflows triggered by workflow_dispatch, push, or schedule would skip comment creation even when a relevant PR existed.

Changes

JavaScript Implementation (add_comment.cjs)

• Added resolveCurrentBranch() to extract branch from GITHUB_REF/GITHUB_HEAD_REF
• Added findOpenPullRequestForBranch() to search for open PRs via GitHub API
• Updated main logic: when triggered by non-commentable events, resolves branch → finds matching PR → comments if found → exits gracefully if not
• Supports target-repo slug for cross-repository scenarios

Go Compiler (add_comment.go)

• Removed job condition requiring github.event.issue.number || github.event.pull_request.number || github.event.discussion.number
• Job now runs whenever add_comment output exists; JavaScript handles target resolution

Behavior

Before:

on: workflow_dispatch
safe-outputs:
  add-comment:  # Would skip with "not in commentable context"

After:

on: workflow_dispatch
safe-outputs:
  add-comment:  # Finds PR for current branch and comments

For workflow_dispatch on branch feature-x with open PR #123:

1. Resolves feature-x from GITHUB_REF
2. Searches for PRs with head: "owner:feature-x"
3. Comments on PR Network Permissions Testing Report - MCP Fetch Tool Analysis #123
4. If no PR found, exits gracefully with log message (no error)

Existing behavior for issue/PR/discussion triggers unchanged.

Test Coverage

• 8 new test cases covering PR resolution, branch resolution, graceful exits, error handling, and target-repo support
• All 23 add_comment tests pass
• All 591 JavaScript tests pass

Original prompt

Update the safe-outputs add-comment JavaScript to handle workflows triggered by non-commentable events (e.g., workflow-dispatch, workflow run). When the activation is not from an issue, discussion, or pull-request:

• Resolve the current branch for the run (e.g., from GITHUB_REF/GITHUB_HEAD_REF or equivalent in the engine).
• Find the first open pull-request whose head branch matches this branch (targeting the same target-repo if applicable).
• If such a pull-request exists, use that pull-request as the comment target and proceed with add-comment.
• If no matching open pull-request is found, do not fail; log a clear message in logs and exit gracefully without commenting.

Notes:

• Preserve existing behavior for issue, discussion, pull-request, and pull-request-comment triggers.
• Ensure safe-outputs handling remains intact and sanitized.
• Respect permissions and github-token scopes.
• Provide verbose logs when verbose is enabled.

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[pelikhan]

@copilot this mode must be enabled by a field on the configuration `