Add Nix flake for mcp and mcp-agent

Exposes two packages:
- default (mcp CLI) for operator workstations
- mcp-agent for managed nodes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/modernc.org/sqlite/tpch.sh

@@ -0,0 +1,20 @@
+set -e
+echo "See http://www.tpc.org/tpc_documents_current_versions/pdf/tpc-h_v2.17.1.pdf for details"
+tmp=$(mktemp -d)
+cd $tmp
+echo "installing modernc.org/sqlite/tpch@latest into $tmp"
+GOBIN=$tmp go install modernc.org/sqlite/tpch@latest
+echo "generating pseudotext"
+./tpch -pseudotext
+for sf in 1 10 ; do
+	for sut in sqlite3 sqlite ; do
+		echo "$sut: generating a $sf GB test DB"
+		time -p ./tpch -sut $sut -dbgen -sf $sf
+		for q in 1 2 ; do
+			echo -n "$sut: running query $q: "
+			./tpch -sut $sut -q $q -sf $sf
+		done
+	done
+done
+cd -
+rm -rf $tmp