matrix: hive-matrix-mcp crate (daemon+stdio bridge) + harness wiring (#548 phase 3)

flake.nix

@@ -93,8 +93,14 @@
             # rsvg-convert call — that whole codepath moved into the
             # `hyperhive-assets` derivation in #555, so the rust
             # derivation no longer needs the dependency.
+            # `sqlite` required by matrix-sdk's `sqlite` feature
+            # (`hive-matrix-mcp` workspace member, #548 phase 3) — the
+            # matrix-sdk-sqlite + rusqlite stack links against system
+            # libsqlite3 by default.
             nativeBuildInputs = [
               pkgs.git
+              pkgs.sqlite
+              pkgs.pkg-config
             ];
           }
         );