Support batch inspection of multiple issues

[gokul-debugger]

Problem

Contributors often shortlist several issues before choosing one. Running contribcheck inspect separately for every candidate is repetitive and makes comparison difficult.

Proposed change

Add a batch command that reads issue references from a text file and inspects them with bounded concurrency.

contribcheck batch candidates.txt
contribcheck batch candidates.txt --json

The input file should contain one GitHub issue URL or shorthand reference per line. Blank lines and lines beginning with # should be ignored.

Acceptance criteria

• Results preserve input order even when requests run concurrently.
• Concurrency is bounded (suggested default: 4 concurrent inspections) to avoid unnecessary GitHub API pressure.
• A failure for one issue is reported for that item without discarding successful reports.
• Human-readable output provides a compact comparison of reference, title, verdict, and key blockers.
• JSON output uses a documented, stable top-level structure.
• The existing --fail-on behavior has a documented batch equivalent: the batch exits non-zero if any item meets the chosen threshold.
• Tests cover parsing, ordering, partial failures, and exit codes without making live GitHub requests.
• The README includes an example input file and command.

Design note

Please propose the JSON result shape and exact exit-code behavior in a comment before implementation, because they become public interfaces.