feat(subject): add pr/issue set-subject via NIP-32 kind-1985 labels

Adds the ability to update the displayed title of a PR or issue after
creation using a kind-1985 label event with the #subject namespace.
Only the author or a repository maintainer may set the subject. The
latest authorised event wins with tiebreak by lexicographically larger
event ID (NIP-1 replaceable event semantics). Branch names and commit
messages are never affected.

- Split get_labels() into process_labels() (additive #t) and
  process_subject() (replaceable-style #subject), with a shared
  get_labels_and_subject() entry point that processes both from a
  single pre-fetched slice of kind-1985 events
- All list/view/JSON display paths apply the subject override silently
- New ngit pr set-subject <id> --subject <text> command
- New ngit issue set-subject <id> --subject <text> command

1 files changed, 1 insertions, 0 deletions

diff --git a/src/bin/ngit/sub_commands/mod.rs b/src/bin/ngit/sub_commands/mod.rs
index 7a3c2b5..db8ea54 100644
--- a/src/bin/ngit/sub_commands/mod.rs
+++ b/src/bin/ngit/sub_commands/mod.rs
@@ -15,5 +15,6 @@ pub mod pr_merge;
 pub mod pr_status;
 pub mod repo;
 pub mod send;
+pub mod set_subject;
 pub mod sync;
 pub mod whoami;