feat(rust): Teams from first-party clans (phase 9, protocol 6)

A first-party Rust clan is a Team (R5). This module becomes the site's
Team provider and answers core from the plugin's `clans` board. Design
of record: docs/modules/rust/PLAN.md §24, D47-D58.

- The store: rust_clans, rust_clan_members and rust_clan_boards. A clan's
  identity is <serverId>:<clanId>:<createdMs> (D52), because the game
  restarts clan ids whenever its clan database version changes.
- The provider (D53): getTeams is complete only when every server's
  board is fresh, supported and untruncated. It is partial when some
  are, and refuses when none are. Freshness is judged by the website's
  clock, from when the board's `t` last advanced.
- Only a complete board may mark a clan gone. A board at the game's
  100-clan ceiling (D55), or one with an unreadable row, proves nothing
  about what it leaves out.
- Leadership is diffed board to board and published (D54). The five clan
  events are published as team.* kinds, and written to the Team feed as
  members-only lines (D49).
- Core only writes feed items for a Team it already holds. So the last 10
  minutes of clan events are re-offered on each board refresh, deduped by
  a sha1 key: core clamps a dedupeKey to 40 characters, and a readable key
  would be truncated into collisions.
- projectRoster and the clan page share one audience rule (D48): the
  clan's linked members and staff by default, re-read from the users row.
  The setting lives on Admin > Rust visibility, which also warns about
  uMod Clans (D47) and the ceiling.
- Public: GET servers/:id/clans (the list is public, D58) and
  GET clans/:externalId. The client adds a Clans tab and
  /rust/clans/:externalId, with three module slots for core's notify,
  activity and forum contributions (D56).
- Linking and unlinking an account ask core to reconcile Teams (D57).
- The clan kinds are staff-class in the public feed allowlist.
- PROTOCOL_VERSION is now 6.

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

server/sidecarClient.js

@@ -52,11 +52,11 @@ const TIMEOUT_MS = 12000
  * here, `PROTOCOL_VERSION` in the sidecar, `ProtocolVersion` in the bridge
  * plugin, and `protocol` in its `overlay.toml`.
  *
- * **5 — configuration from the site.** Protocol 2 was the read path, 3 the
- * first message the WEBSITE originates (`link.confirm`), 4 the first that
- * writes to the game's permission store; 5 is the first that writes to the game
- * HOST'S FILESYSTEM — a plugin's settings, and a reload watched closely enough
- * to be undone. The bump lands here in the same change as the emitters,
+ * **6 — first-party clans.** Protocol 2 was the read path, 3 the first
+ * message the WEBSITE originates (`link.confirm`), 4 the first that writes to
+ * the game's permission store, 5 the first that writes to the game HOST'S
+ * FILESYSTEM; 6 adds the `clans` board and five clan events core's Teams are
+ * built from, and no route at all. The bump lands here in the same change as the emitters,
  * because the sidecar refuses a client declaring a different version with a
  * `409`: a module left on 2 would stop being able to read the server board it
  * has been reading all along. A constant that lags the deployment is not a safe
@@ -66,7 +66,7 @@ const TIMEOUT_MS = 12000
  * deployment into a `409` naming both numbers instead of a parse failure three
  * layers further in.
  */
-const PROTOCOL_VERSION = 5
+const PROTOCOL_VERSION = 6
 
 /** What a caller gets back. Shaped once so every call site reads the same. */
 function reply(ok, status, data = null) {