feat(web): vercel deployment and vds compose/systemd setup

Add Vercel config with React Router preset, vercel-build script and
/api/auth rewrite to the Convex site. Add VDS staging compose for the
Rivet engine and runner plus systemd units, deployment plan, and
Docker/Vercel ignore rules. Lockfile covers both the web and agents
dependency additions.

deploy/compose/Caddyfile

@@ -0,0 +1,63 @@
+# Caddy reverse proxy for the Zopu VDS staging agent stack.
+#
+# This is the ONLY public ingress to the private worker (see
+# docs/DEPLOYMENT_PLAN.md §"Public surface"). It terminates TLS for the Flue
+# callback hostname that Convex reaches, then forwards ONLY the documented agent
+# worker paths to the internal `agents` service.
+#
+# Hard rules this file enforces:
+#   - No generic /api/* proxy and no browser-to-Flue traffic (DEPLOYMENT_PLAN.md
+#     line 86). Browsers talk only to Convex.
+#   - Only the Flue Node worker paths Convex actually calls are routed:
+#       /agents/zopu/<organizationId>      conversation admission
+#       /internal/work-attempts/*           work attempt execute + cancel
+#       /api/rivet/*                        RivetKit Actor gateway surface
+#       /workflows/*                        Flue workflow execution
+#       /health                             liveness probe (Compose healthcheck/CI)
+#   - Everything else returns 404. The private worker protocol stays narrow.
+#
+# Variables are injected by the `caddy` Compose service environment:
+#   {$AGENTS_HOST}     public hostname, e.g. agents-staging.example.com
+#   {$AGENTS_UPSTREAM} internal upstream host:port, e.g. agents:3000
+#   {$ACME_EMAIL}      email for the Let's Encrypt account
+#
+# TLS certs and the ACME account persist in the caddy-data volume. Caddy serves
+# its own ACME HTTP-01 challenge responses on :80 automatically, so the :80
+# block below only redirects everything else to HTTPS — worker traffic is never
+# served over plain HTTP.
+{
+	email {$ACME_EMAIL}
+}
+
+# --- TLS termination for the Flue callback hostname ---------------------------
+{$AGENTS_HOST} {
+	encode zstd gzip
+
+	# Conversation admission: Convex POSTs to /agents/zopu/<organizationId>.
+	# The conversationRoute middleware requires the FLUE_DB_TOKEN bearer and the
+	# matching x-zopu-organization-id header.
+	reverse_proxy /agents/zopu/* {$AGENTS_UPSTREAM}
+
+	# Internal work-attempt execute/cancel. Requires the internalRoute bearer.
+	reverse_proxy /internal/work-attempts/* {$AGENTS_UPSTREAM}
+
+	# RivetKit Actor gateway surface (app.all("/api/rivet/*")). Routed so the
+	# runtime registry handler is reachable for actor metadata/start.
+	reverse_proxy /api/rivet/* {$AGENTS_UPSTREAM}
+
+	# Flue workflow execution (workflows/plan-work). Requires the workflowRoute
+	# bearer + x-zopu-organization-id header.
+	reverse_proxy /workflows/* {$AGENTS_UPSTREAM}
+
+	# Caddy routes the liveness request to the actual worker; it must not mask a
+	# failed worker process with a synthetic successful response.
+	reverse_proxy /health {$AGENTS_UPSTREAM}
+
+	# Everything else is not part of the private worker protocol.
+	respond 404
+}
+
+# --- HTTP → HTTPS redirect (Caddy still answers ACME challenges on :80) -------
+:80 {
+	redir https://{host}{uri} permanent
+}