Restrict flyio-proxy ACLs to dedicated tag:flyio-target endpoints (#126)

## Summary
- Introduce `tag:flyio-target` so services must explicitly opt in to be reachable by the fly.io proxy
- Replace broad `tag:k8s` and `tag:homelab` grants with the new tag in the ACL rule and test
- Add `tailscale.com/tags: "tag:k8s,tag:flyio-target"` annotation to docs, loki, and prometheus Ingresses
- Switch Alloy push endpoints from `*.ops.eblu.me` (Caddy) to `*.tail8d86e.ts.net` (Tailscale Ingress)
- Update docs: flyio-proxy, caddy, tailscale, forgejo (future public access + security checklist), expose-service-publicly

## Manual step (not in PR)
Update the k8s operator OAuth client in the Tailscale admin console to include `tag:flyio-target` in its scope. Without this, the operator cannot assign the new tag to Ingress proxy nodes.

## Deployment order
1. **Pulumi ACLs** — `mise run tailnet-preview && mise run tailnet-up`
2. **OAuth client** — Manual update in Tailscale admin console
3. **K8s Ingresses** — `argocd app sync apps && argocd app sync docs loki prometheus`
4. **Fly.io proxy** — `mise run fly-deploy`
5. **Verify** — `mise run services-check`, check Grafana dashboards

## Test plan
- [ ] `mise run tailnet-preview` shows clean diff
- [ ] `argocd app diff docs`, `argocd app diff loki`, `argocd app diff prometheus` show only annotation additions
- [ ] After deploy: Grafana dashboards show continued log/metric flow
- [ ] `curl -sf https://docs.eblu.me` returns 200
- [ ] `mise run services-check` passes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/126

docs/reference/services/flyio-proxy.md

@@ -71,11 +71,11 @@ Alloy listens on `127.0.0.1:12345` for self-scraping its `/metrics` endpoint. Al
 
 ## Security Considerations
 
-The `tag:flyio-proxy` ACL grants access to both `tag:k8s:443` (for proxying public services) and `tag:homelab:443` (for pushing metrics/logs to [[caddy|Caddy]]-proxied Loki and Prometheus). This means a compromised nginx config could route traffic to **any** Caddy-proxied service — not just the intended backends. Some of those services (Loki, Prometheus) have no auth; others ([[forgejo]], [[navidrome]], [[immich]]) do.
+The `tag:flyio-proxy` ACL grants access only to `tag:flyio-target:443`. Services must explicitly opt in by adding a `tailscale.com/tags: "tag:k8s,tag:flyio-target"` annotation to their Tailscale Ingress. This means the proxy can only reach endpoints that have been individually tagged — a compromised nginx config cannot route to arbitrary services on the tailnet.
 
-Exploitation requires either pushing a malicious image to Fly.io or modifying the nginx config — both of which require RCE on [[gilbert]] (where `fly` is authenticated) or access to [[1password]] (the deploy token). This is an acceptable boundary given that 1Password is already the trust root for the entire infrastructure.
+Currently tagged as `tag:flyio-target`: [[docs]], [[loki]], [[prometheus]]. Loki and Prometheus are tagged so that [[alloy|Alloy]] (running inside the container) can push logs and metrics directly via their Tailscale Ingress endpoints — the restricted ACL means Caddy on indri (`tag:homelab`) is not reachable from the proxy.
 
-If this surface area becomes a concern, an alternative would be to add dedicated Tailscale Ingress tags for Loki/Prometheus write endpoints and restrict `tag:flyio-proxy` to only those.
+To expose an additional service through the proxy, add the `tag:flyio-target` annotation to its Tailscale Ingress. See [[expose-service-publicly]] for the full workflow.
 
 ## Secrets