Add swamp issue get CLI command to fetch issue details

Problem

The swamp CLI can submit issues (swamp issue bug, swamp issue feature) but has no command to fetch and display an existing issue's details. The issue-lifecycle model can fetch issues, but there's no lightweight CLI command for quick lookups.

This is needed so that workflows (like checking whether an issue author is a team member before co-authoring a commit) can be performed directly from the CLI without creating a full lifecycle model instance.

Proposed Solution

Add a swamp issue get <number> command that:

• Fetches issue details from GET /api/v1/lab/issues/{number}
• Displays title, type, status, author (once #117 lands), body, assignees, and comment count
• Supports both log and json output modes
• Requires swamp auth login (same as issue submission)

Example usage:

swamp issue get 42
swamp issue get 42 --json

Affected Components

• New CLI command: swamp issue get (src/cli/commands/)
• Presentation layer: new output renderer for issue details
• Infrastructure: may reuse the existing SwampClubClient or add a fetchIssue method to the auth/submission client

Depends on #117 for the author field, but the command is useful without it.