feat: password Realm, single-chair login, shared parliament context (0.9.12)

Derive Realm keys from a user password (Argon2id, no private key on disk).
Login claims the sole chair with handover; peers share parliament context;
--new-project clears it. CLI peer/discover helpers and Docker alpine recipe
included; headless empty-answer retries raised for unattended runs.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/settings.c

@@ -51,6 +51,8 @@ int cst_settings_load(cst_settings_t *s) {
            cJSON_GetObjectItemCaseSensitive(root, "mode"));
   copy_str(s->approval, sizeof(s->approval),
            cJSON_GetObjectItemCaseSensitive(root, "approval"));
+  copy_str(s->collaboration, sizeof(s->collaboration),
+           cJSON_GetObjectItemCaseSensitive(root, "collaboration"));
   s->show_thinking =
       cJSON_IsTrue(cJSON_GetObjectItemCaseSensitive(root, "show_thinking"));
   const cJSON *tr = cJSON_GetObjectItemCaseSensitive(root, "trusted_workspaces");
@@ -111,6 +113,8 @@ int cst_settings_save(const cst_settings_t *s) {
     cJSON_AddStringToObject(root, "mode", s->mode);
   if (s->approval[0])
     cJSON_AddStringToObject(root, "approval", s->approval);
+  if (s->collaboration[0])
+    cJSON_AddStringToObject(root, "collaboration", s->collaboration);
   if (s->show_thinking)
     cJSON_AddTrueToObject(root, "show_thinking");
   if (s->ntrusted) {