Add demo scripts: egress IP check and bulk proxy creation

docs/demo/show-egress-ips.sh probes each healthy proxy from the
discovery API against an IP-echo site; create-kubernetes-proxies.sh and
create-gcp-proxies.sh bulk-create demo Proxies, the gcp one spreading
them across randomly picked EU zones.

Co-Authored-By: Claude <noreply@anthropic.com>

docs/plans-executions/2026-08-11-2220-demo-scripts.md

@@ -0,0 +1,38 @@
+# Execution: Demo scripts
+
+Plan: [2026-08-11-2220-demo-scripts.md](../plans/2026-08-11-2220-demo-scripts.md)
+
+- [x] Step 0 — Branch `feat/demo-scripts` + plan commit
+- [x] Step 1 — `docs/demo/show-egress-ips.sh`
+- [x] Extra (added iteratively, not in the original plan) — proxy-creation scripts
+
+## Step 0 + Step 1
+
+Branched off `main`, committed the plan alone, then wrote
+`docs/demo/show-egress-ips.sh`: takes `BASE_URL` as its argument, lists
+`/v1/proxies` (bearer auth via optional `TOKEN` env), probes each healthy
+proxy with `curl -x http://ip:port` against an IP-echo site
+(`IP_ECHO_URL`, default ipify JSON), banners which proxy each request goes
+through, skips unhealthy ones, and ends with a probed/skipped/failed
+summary. Per user request the script was left uncommitted for iteration
+and no verification beyond `bash -n` was run.
+
+## Extra — create-kubernetes-proxies.sh, create-gcp-proxies.sh
+
+Added on the same branch before the first commit:
+
+- `create-kubernetes-proxies.sh <count>` — creates
+  `proxy-kubernetes-demo-1..N` with the kubernetes provider, spec taken
+  from `config/samples/proxy_kubernetes.yaml`, applied via
+  `kubectl apply -f -` heredocs. Optional `NAMESPACE` env.
+- `create-gcp-proxies.sh <count>` — creates `proxy-gcp-demo-1..N` from the
+  user-supplied gcp-eu manifest (e2-micro, Ubuntu 24.04, Squid
+  cloud-init), each with a zone picked randomly from a hardcoded list of
+  27 EU zones so the fleet gets egress IPs from different locations.
+  Env overrides: `ZONES`, `GCP_PROVIDER` (default `gcp-eu`), `NAMESPACE`.
+
+Worth noting: beyond the user's sample manifest, the gcp script also
+writes the picked zone into `attributes.zone`, so the discovery API
+exposes each proxy's location and leases can select on it. The zone list
+is static — if a project lacks quota in some region, `ZONES` narrows the
+pool; nothing validates zones against the live project.