Add `--assignee` flag to `isq issue list`

[camwest]

Context

When using isq with AI agents like Claude Code, the agent often tries isq issue list --assignee @me instead of --mine.

Error message:

error: unexpected argument '--assignee' found
tip: a similar argument exists: '--unassigned'

Proposal

Add --assignee <user> flag that:

• Accepts a username to filter by assignee
• Supports @me as a special value (equivalent to --mine)

Implementation

• Add --assignee option to the list command
• When value is @me, treat it as equivalent to --mine
• Otherwise filter by the specified username

🤖 Generated with Claude Code