feat(cover-note): add kind-1624 cover notes for PRs, patches, and issues

Implements experimental kind-1624 cover note events:

- KIND_COVER_NOTE constant and process_cover_note() in git_events.rs;
  replaceable semantics (latest created_at, hex-id tiebreak), author or
  maintainer only
- kind-1624 events fetched alongside labels in the fetch pipeline;
  cover_notes count added to FetchReport display
- ngit pr/issue view: cover note displayed in place of description with
  a clear 'Cover Note:' header; maintainer-authored notes identify the
  author; original description shown only with --comments; cover_note
  object included in --json output
- ngit pr set-cover-note / ngit issue set-cover-note: publish a
  kind-1624 event; nostr: mentions in --body converted to q/p tags via
  tags_from_content (same rules as issue --body)
- Fix pre-existing clippy::too_many_lines on repo/mod.rs show_info

1 files changed, 2 insertions, 0 deletions

diff --git a/skills/ngit/SKILL.md b/skills/ngit/SKILL.md
index 5c17a70..186341e 100644
--- a/skills/ngit/SKILL.md
+++ b/skills/ngit/SKILL.md
@@ -127,6 +127,7 @@ ngit pr ready <ID|nevent> --reason "addressed review feedback"
 ngit pr draft <ID|nevent> --reason "needs more work"
 ngit pr label <ID|nevent> --label bug --label enhancement
 ngit pr set-subject <ID|nevent> --subject "New title"
+ngit pr set-cover-note <ID|nevent> --body "Updated description. See nostr:nevent1abc…"
 ```
 
 ## Issues
@@ -146,6 +147,7 @@ ngit issue resolved <ID|nevent> --reason "fixed in abc123"
 ngit issue reopen <ID|nevent> --reason "regression in v2.3"
 ngit issue label <ID|nevent> --label bug --label enhancement
 ngit issue set-subject <ID|nevent> --subject "New title"
+ngit issue set-cover-note <ID|nevent> --body "Updated description. See nostr:nevent1abc…"
 ```
 
 ## Account management