feat(bridge): protocol 6 — first-party clans, one board and five events

The `clans` board carries every clan the game will list, with its roster
and roles, plus the facts the website needs to trust it: enabled,
backend, supported, truncated, and whether the optional uMod Clans
plugin is loaded. It is re-sent on connect and on the 60-second cadence,
and a few seconds after any membership change. The five events are
clan.created, clan.disbanded, clan.member.added, clan.member.left and
clan.member.kicked.

What the game's assemblies dictated:
- The game has no enumerate-all call. The clan leaderboard is the only
  listing, and the game clamps it to 100 clans. A board at that ceiling
  says `truncated`, as does one that would not fit in 768 KiB (the
  sidecar drops lines over 1 MiB).
- The local backend is synchronous behind ValueTask. A task that has not
  completed means another backend (Nexus), which is refused with a reason
  rather than waited on from the main thread.
- A clan id is not an identity, so every frame carries createdMs.
- OnClanMemberAdded hands over a bare id before the game's cache
  refreshes, so the clan is read back, with a fallback to the id alone.
- uMod Clans raises OnClanDisbanded(string, List<ulong>), which has the
  same name and arity as the game's hook, so the bridge types it exactly.

A member's LastSeen is never sent: it is presence (PLAN.md §23).
overlay.toml moves to protocol 6 and drops Clans from requires_plugins
(D47): Teams come from the game's own clans.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

overlay.toml

@@ -26,9 +26,9 @@
 # the same change that alters the emitters, exactly as the sidecar bumps
 # PROTOCOL_VERSION and the module bumps its own constant.
 #
-# Current: 5 — the transport, the read path, identity, the permission mirror, and
-# configuration from the site (docs/rust-link/PROTOCOL.md §11).
-protocol = 5
+# Current: 6 — the transport, the read path, identity, the permission mirror,
+# configuration from the site, and first-party clans (docs/rust-link/PROTOCOL.md §12).
+protocol = 6
 
 # ── Oxide compatibility ──────────────────────────────────────────────────────
 #
@@ -45,6 +45,11 @@ min_oxide_version = "2.0.7585"
 # The `oxide/plugins/` files this overlay expects to find already installed. They
 # are not shipped here — they are third-party plugins an operator installs from
 # uMod — and the installer's `doctor` reports a missing one rather than
-# installing it. Listing them is what turns "the site shows no clans" into a
+# installing it. Listing them is what turns a missing reward or zone into a
 # named prerequisite.
-requires_plugins = ["Clans", "Kits", "PopupNotifications", "ZoneManager"]
+#
+# The uMod **Clans** plugin is deliberately NOT listed (docs/modules/rust/PLAN.md
+# D47). Teams come from Rust's own clan system, which that plugin never touches,
+# so requiring it would split a server's players across two unrelated clan
+# systems. It belongs to phase 17's optional tier.
+requires_plugins = ["Kits", "PopupNotifications", "ZoneManager"]