Add Fly.io public reverse proxy for docs.eblu.me (#120)

## Summary

- Adds a Fly.io reverse proxy (`blumeops-proxy`) that tunnels public traffic to homelab services over Tailscale
- First service exposed: `docs.eblu.me` — the Quartz static docs site
- Includes Pulumi IaC for Tailscale auth key/ACLs and Gandi DNS CNAME
- Adds mise tasks (`fly-deploy`, `fly-setup`, `fly-shutoff`) and Forgejo CI workflow

## Key details

- Fly.io Firecracker VMs support TUN devices natively — no userspace networking needed
- Tailscale auth key is `preauthorized=True` to avoid device approval hangs on container restarts
- nginx caches aggressively for the static site; health check is on the default_server block
- ACLs restrict `tag:flyio-proxy` to `tag:k8s` on port 443 only
- DNS CNAME deployed and verified: `docs.eblu.me` → `blumeops-proxy.fly.dev`

## Test plan

- [x] `curl -sf https://blumeops-proxy.fly.dev/healthz` returns `ok`
- [x] `curl -I -H "Host: docs.eblu.me" https://blumeops-proxy.fly.dev/` returns 200 with `X-Cache-Status`
- [x] `curl -I https://docs.eblu.me/` returns 200 with valid Let's Encrypt cert
- [x] `dig forge.ops.eblu.me` still resolves to 100.98.163.89 (private services unaffected)
- [x] Set `FLY_DEPLOY_TOKEN` Forgejo Actions secret for CI auto-deploy

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

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/120

pulumi/gandi/__main__.py

@@ -54,8 +54,22 @@ base_record = gandi.livedns.Record(
     values=[tailscale_ip],
 )
 
+# ============== Public Services (Fly.io proxy) ==============
+# CNAME records pointing public subdomains to Fly.io for reverse proxying
+# back to the tailnet. See docs/how-to/expose-service-publicly.md
+
+docs_public = gandi.livedns.Record(
+    "docs-public",
+    zone=domain,
+    name="docs",
+    type="CNAME",
+    ttl=300,
+    values=["blumeops-proxy.fly.dev."],
+)
+
 # ============== Exports ==============
 pulumi.export("domain", domain)
 pulumi.export("wildcard_fqdn", f"*.{subdomain}.{domain}")
 pulumi.export("base_fqdn", f"{subdomain}.{domain}")
 pulumi.export("target_ip", tailscale_ip)
+pulumi.export("docs_public_fqdn", f"docs.{domain}")