feat(label): add `ngit issue label` and `ngit pr label` commands

Publishes a NIP-32 kind-1985 label event referencing the target issue or
PR. Only the event author or a repository maintainer may apply labels.
Duplicate labels (already present via t-tags or prior kind-1985 events)
are silently skipped. The new event is saved to the local cache before
broadcasting so subsequent reads reflect the change immediately.

CLI:
  ngit issue label <id> --label <L> [--label <L>...]
  ngit pr label <id> --label <L> [--label <L>...]

1 files changed, 24 insertions, 0 deletions

diff --git a/src/bin/ngit/cli.rs b/src/bin/ngit/cli.rs
index ccf25bb..b9b274e 100644
--- a/src/bin/ngit/cli.rs
+++ b/src/bin/ngit/cli.rs
@@ -301,6 +301,18 @@ pub enum PrCommands {
         #[arg(long)]
         offline: bool,
     },
+    /// add one or more labels to a PR (author or maintainer only)
+    Label {
+        /// Proposal event-id (hex) or nevent (bech32)
+        #[arg(value_name = "ID|nevent")]
+        id: String,
+        /// Label to apply (repeatable: --label bug --label help-wanted)
+        #[arg(long = "label", value_name = "LABEL", required = true)]
+        labels: Vec<String>,
+        /// Use local cache only, skip network fetch
+        #[arg(long)]
+        offline: bool,
+    },
 }
 
 // ---------------------------------------------------------------------------
@@ -395,6 +407,18 @@ pub enum IssueCommands {
         #[arg(long)]
         offline: bool,
     },
+    /// add one or more labels to an issue (author or maintainer only)
+    Label {
+        /// Issue event-id (hex) or nevent (bech32)
+        #[arg(value_name = "ID|nevent")]
+        id: String,
+        /// Label to apply (repeatable: --label bug --label help-wanted)
+        #[arg(long = "label", value_name = "LABEL", required = true)]
+        labels: Vec<String>,
+        /// Use local cache only, skip network fetch
+        #[arg(long)]
+        offline: bool,
+    },
 }
 
 #[derive(Subcommand)]