feat: fetch and report NIP-34 issues and their statuses

Download kind-1621 issues from relays into the local cache alongside
patches and PRs. Issue IDs are tracked separately from proposal IDs
throughout the fetch pipeline so they never appear in proposal lists.

- get_fetch_filters: include Kind::GitIssue in the #a-tag filter and
  add a dedicated issue_ids parameter to fetch status events (1630-1633)
  tagged with known issue IDs
- FetchRequest: add issue_ids field populated from the local cache
- fetch_all_from_relay: track fresh_issue_roots independently of
  fresh_proposal_roots; loop continues until both are drained
- process_fetched_events: route GitIssue events into fresh_issue_roots
  and report.issues; route status events to issue_statuses or statuses
  based on whether the root ID is a known issue or proposal
- FetchReport: add issues and issue_statuses fields, consolidated across
  relays, and displayed as "N issue(s), M issue status(es)" in the report

0 files changed, 0 insertions, 0 deletions