M5: moderation, permissions, channel CRUD, in-app account management

- Server-side moderation & permissions (kick/ban/move/server-mute, channel CRUD).

- Database schema v2: channels, bans; BLAKE2b channel passwords, Argon2id accounts.

- C ABI additions and client-side handling (vc_kick_user, vc_ban_user, vc_set_permission, vc_set_server_mute, vc_move_user, vc_create/edit/delete_channel, vc_create/reset/delete/list_account).

- vccli flags for all M5 operations plus --username/--password auth.

- Four new tests covering permissions, kick/ban/move/mute, admin accounts, channel CRUD.

- Docs: protocol.md envelope updates, security.md channel-password hashing, PROGRESS.md.

docs/protocol.md

@@ -92,6 +92,7 @@ message Envelope {
     KickRequest       kick                = 60;
     BanRequest        ban                 = 61;
     SetPermissionRequest set_permission   = 62;
+    ServerMuteRequest server_mute         = 63;
 
     // ── Admin account management (privileged) ─────────────
     // Accounts are admin-provisioned (no self-serve registration in v1).
@@ -100,6 +101,7 @@ message Envelope {
     ResetPasswordRequest reset_password   = 71;
     DeleteAccountRequest delete_account   = 72;
     ListAccountsRequest  list_accounts    = 73;
+    ListAccountsResult   list_accounts_result = 74;
 
     // ── Extension escape hatch ────────────────────────────
     Extension         extension           = 200;  // {string ns; bytes payload;}
@@ -224,6 +226,7 @@ message User {
   bool   self_deafened = 6;
   bool   server_muted = 7;
   repeated StreamInfo streams = 8;     // active media streams this user publishes
+  bool   server_deafened = 9;          // M5: server-imposed deafen
 }
 
 message StreamInfo {
@@ -268,7 +271,8 @@ message TextMessage {
   server→client events use `request_id = 0`.
 - **`GenericResult { bool ok; uint32 code; string message; }`** is the default
   acknowledgement for operations without a richer reply (create/edit/delete channel, move
-  user, etc.). Error `code`s are an enumerated, stable list.
+  user, kick, ban, server-mute, set-permission, create/reset/delete account). Error `code`s
+  are an enumerated, stable list.
 - Fatal conditions send **`Disconnect { code; reason }`** then close the TLS connection.
 
 ## 7. Keepalive & timeouts