feat: parliament seat collaboration loop (0.9.19)

Seats publish via parliament_note, sync pushes on write, member join without
stealing the chair, and worker tools are hard-gated when parliament is active.

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

tests/test_registry.c

@@ -138,11 +138,11 @@ int main(void) {
   }
 
   cJSON *all = cst_tools_schema_cfg(&cfg);
-  /* Every tool the host can actually run is offered in the default profile;
-   * one whose platform probe fails (the clipboard without a helper) is not. */
+  /* Every tool active for this config is offered; platform-unavailable tools
+   * and mode-gated tools (e.g. parliament_note outside parliament) are not. */
   int usable = 0;
   for (int i = 0; i < cst_tool_count(); i++)
-    if (cst_tool_available(cst_tool_at(i), NULL, 0) == 0)
+    if (cst_tool_active(&cfg, cst_tool_at(i)))
       usable++;
   EXPECT(cJSON_GetArraySize(all) == usable, "default: every usable tool");
   EXPECT(schema_has(all, "edit_file") && schema_has(all, "grep") &&