Add batch issue update and dry-run support

[dubscode]

Summary

Please add batch update support, ideally with a dry-run mode, for common issue maintenance workflows.

Proposed command shapes

A few possible designs:

linear issues update --ids BB-426,BB-427 --input '{"priority":2}' --json
linear issues bulk-update --ids BB-426,BB-427 --input '{"stateId":"..."}' --json
linear issues bulk-update --input-file updates.json --dry-run --json

For per-issue updates, an input file could be shaped like:

[
  { "id": "BB-426", "title": "Evalite tracer", "description": "..." },
  { "id": "BB-427", "title": "Eval tracing", "description": "..." }
]

Why this matters

A lot of Linear maintenance happens in batches: retitling sub-issues, normalizing priorities, moving a set into a cycle, assigning related issues, or updating descriptions after a planning session.

Right now each issue update has to be a separate command. That is workable for one or two issues, but clunky for agents and scripts when the user wants a reviewable bulk pass.

Expected behavior

• --dry-run should show the intended changes without writing them.
• JSON output should report per-issue success/failure.
• Partial failures should be explicit and machine-readable.
• Batch update should not remove append-only relations unless explicit removal fields are supplied.