Consolidate collect-issues-shared.yml and collect-pull-requests-shared.yml into one shared workflow

[ineedjet]

Summary

We currently maintain two nearly identical reusable workflows:

• .github/workflows/collect-issues-shared.yml — wraps actions/collect-issues
• .github/workflows/collect-pull-requests-shared.yml — wraps actions/collect-pull-requests

Both take the exact same inputs (organizations, repositories, project_owner, project_number) and the same token secret, and only differ in which action they call. As part of the broader effort to consolidate Shared Workflows, these two should be merged into a single collect-shared.yml workflow that can collect issues, pull requests, or both, depending on the config passed to it.

Proposed approach

Add a workflow input (e.g. collect: issues | pull_requests | both, or two booleans collect_issues / collect_pull_requests) that controls which of the underlying actions run. The collect job would conditionally run the collect-issues and/or collect-pull-requests action steps (or use a matrix) based on that input, reusing the existing organizations, repositories, project_owner, project_number, and token inputs/secrets as-is.

Acceptance criteria

• A single shared workflow (e.g. collect-shared.yml) can be called to collect only issues, only pull requests, or both in one run, based on its inputs.
• No change in behavior/output for callers that only need issues or only need pull requests.
• collect-issues-shared.yml and collect-pull-requests-shared.yml are removed once callers are migrated (or kept as thin wrappers around the new workflow if a deprecation period is preferred).
• README / usage docs updated to reflect the new shared workflow and its inputs.
• Existing consumers of the two workflows are updated to call the new one.