fix: show issue documents in issue view

[schpetbot]

Summary

• fetch issue documents alongside attachments in issue view
• render a Documents section in terminal output
• include documents in --json output and cover it with tests

Testing

• NO_COLOR=1 deno task test test/commands/issue/issue-view.test.ts
• deno task check
• deno lint
• manual QA against real CLI team issues CLI-85 and CLI-86

Fixes #183