fix: gitea boot persistence via quadlet (incident 2026-08-16)

unattended-upgrades rebooted dankclaw at 15:01; the legacy
podman-compose gitea stack had no systemd units, so rootless podman
did not auto-start the containers. Gitea was down ~1 hour.

- add quadlet units (dankclaw/gitea/quadlet/): gitea-postgres,
  gitea-server, gitea-caddy + gitea.network (DNS enabled; the default
  rootless podman network has dns_enabled=false)
- add gitea stack Caddyfile (upstream gitea-server:3000) and
  .env.example; live password stays in /opt/gitea/.env (0600)
- fix latent name bugs in main stack config: DATABASE_HOST
  gitea-postgres, Caddyfile upstream gitea-server
- docs: rewrite Gitea page for the quadlet stack (management, boot
  persistence, secrets, gotchas, incident log); fix port 3000 in
  stack table; Postgres connection notes
- legacy compose retired on target to /opt/gitea/.deprecated/

dankclaw/gitea/quadlet/gitea.network

@@ -0,0 +1,10 @@
+# Quadlet network: private bridge for the Gitea stack (rootless).
+#
+# Install path on dankclaw: ~/.config/containers/systemd/gitea.network
+# Unit name: gitea-network.service (podman network name: systemd-gitea)
+#
+# DNS is enabled by default for quadlet networks. This matters: the
+# automatic "podman" default network has dns_enabled=false, so container
+# names (gitea-postgres, gitea-server, gitea-caddy) would not resolve.
+
+[Network]