feat(relay): channel labels as t tags on group-state events

A channel can carry up to 8 labels that group channels across channel
types. kind:9007 sets them with ["t", <label>] tags. On kind:9002 the t
tags replace the whole set, a lone ["t", ""] clears it, and an edit
without t tags leaves the set unchanged. Only an owner or admin may change
labels.

The relay refuses, before storage, a label that is not 1-64 characters
from a-z, 0-9, '.', ':' and '-', a label equal to a channel type name, an
empty label mixed with other labels, and more than 8 distinct labels.

Migration 0061 adds channels.labels (TEXT[], default empty, at most 8).
The relay publishes each label as a t tag after the channel type tag on
kinds 39000, 39001 and 39002, and buzz-admin reconcile does the same.
Clients read the first t value as the type; the CLI and buzz-acp parsers
used the last one and now use the first.

Signed-off-by: Logan Johnson <loganj@squareup.com>
Co-authored-by: Larry <627498bd4bd1f281a16431e3c6cce3b5c25b6692798c78672298aefbf2f8f8b5@buzz.block.builderlab.xyz>

crates/buzz-cli/src/commands/channels.rs

@@ -192,7 +192,8 @@ impl ChannelSummary {
             match key {
                 "d" => channel_id = val.map(str::to_string),
                 "name" => name = val.map(str::to_string),
-                "t" => channel_type = val.map(str::to_string),
+                // The first `t` is the channel type; later `t` tags are labels.
+                "t" if channel_type.is_none() => channel_type = val.map(str::to_string),
                 // NIP-29 emits both `private` and `public` (Buzz adds the latter).
                 // The presence of either tag is the source of truth; tag value is unused.
                 "private" => visibility = Some("private".to_string()),
@@ -2008,6 +2009,19 @@ mod tests {
         }
     }
 
+    #[test]
+    fn from_event_reads_the_type_from_the_first_t_tag() {
+        let ev = event(json!([
+            ["d", "11111111-1111-1111-1111-111111111111"],
+            ["name", "labeled"],
+            ["t", "forum"],
+            ["t", "workspace"],
+            ["P", "ab".repeat(32)],
+        ]));
+        let s = ChannelSummary::from_event(&ev).expect("parse");
+        assert_eq!(s.channel_type.as_deref(), Some("forum"));
+    }
+
     #[test]
     fn from_event_extracts_known_tags() {
         let ev = event(json!([