Add top-level `sentry feedback` commands for managing User Feedback

[betegon]

Summary

Add a top-level sentry feedback command group to inspect and manage User Feedback for a Sentry organization, similar to sentry issue.

This is separate from the existing sentry cli feedback command, which submits feedback about the CLI itself.

Modern User Feedback is backed by issues. The implementation should use the organization Issues API with a mandatory issue.category:feedback filter, not the legacy User Reports endpoints.

Command roadmap

First PR

• sentry feedback list [<org>/<project>] — list and search feedback with pagination and unresolved/resolved/spam mailboxes
• sentry feedback view [<org>/<project>/]<feedback-id> — show the feedback issue plus its latest event context; make view the default and expose the standard show alias

Follow-ups

• sentry feedback resolve <feedback-id>
• sentry feedback unresolve <feedback-id> (reopen alias)
• sentry feedback spam <feedback-id>
• sentry feedback unspam <feedback-id> (restore alias)
• sentry feedback mark-read <feedback-id>
• sentry feedback mark-unread <feedback-id>
• sentry feedback assign <feedback-id> <user-or-team>
• sentry feedback unassign <feedback-id>
• sentry feedback comment <feedback-id> — add an internal comment; editing/deleting comments can follow
• sentry feedback delete <feedback-id>
• sentry feedback summary [<org>/<project>] — AI summary when available
• sentry feedback categories [<org>/<project>] — AI-generated categories when available

The first implementation PR should only cover list and view; this issue tracks the full command group.