Db, first commit of work

This also touches atproto/src/lib.rs which may be a problem for the
rebase~

Adds migrations and all the other stuff.

flake.nix

@@ -42,6 +42,7 @@
           packages = (with pkgs; [
             # The package provided by our custom overlay. Includes cargo, Clippy, cargo-fmt,
             # rustdoc, rustfmt, and other tools.
+            sqlx-cli
             rustToolchain
           ]) ++ pkgs.lib.optionals pkgs.stdenv.isDarwin (with pkgs; [ libiconv ]);
         };