Add FlowAgent entrypoint: non-interactive az login via Pattern C secrets

Reads the three _FILE-convention secrets (mounted by Swarm from Docker secrets
provisioned by Woodpecker — see secrets/flowagent.secrets.example), performs
`az login --service-principal`, then execs into whatever command mcpo invokes
(node /app/flowagent/mcp.mjs). No secret value is ever written to disk outside
the ephemeral Docker secret mount, logged, or baked into the image.

mcpo/flowagent/entrypoint.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+# FlowAgent MCP entrypoint — non-interactive Azure service-principal login.
+#
+# Expects three env vars pointing at Docker secret files (Pattern C,
+# _FILE convention, provisioned by Woodpecker — never hand-typed):
+#   FLOWAGENT_AZURE_CLIENT_ID_FILE
+#   FLOWAGENT_AZURE_TENANT_ID_FILE
+#   FLOWAGENT_AZURE_CLIENT_SECRET_FILE
+#
+# On success, execs into the real command (node /app/flowagent/mcp.mjs),
+# replacing this shell so mcpo's stdio pipe talks directly to the MCP process.
+set -eu
+
+: "${FLOWAGENT_AZURE_CLIENT_ID_FILE:?FLOWAGENT_AZURE_CLIENT_ID_FILE not set}"
+: "${FLOWAGENT_AZURE_TENANT_ID_FILE:?FLOWAGENT_AZURE_TENANT_ID_FILE not set}"
+: "${FLOWAGENT_AZURE_CLIENT_SECRET_FILE:?FLOWAGENT_AZURE_CLIENT_SECRET_FILE not set}"
+
+CLIENT_ID="$(cat "$FLOWAGENT_AZURE_CLIENT_ID_FILE")"
+TENANT_ID="$(cat "$FLOWAGENT_AZURE_TENANT_ID_FILE")"
+CLIENT_SECRET="$(cat "$FLOWAGENT_AZURE_CLIENT_SECRET_FILE")"
+
+az login --service-principal \
+  -u "$CLIENT_ID" \
+  -p "$CLIENT_SECRET" \
+  --tenant "$TENANT_ID" \
+  --output none
+
+unset CLIENT_SECRET
+
+exec "$@"