Rewrite PIA VPN as multi-container bridge architecture

Replace the single VPN container (veth pair, host-side auth scripts) with a
multi-container setup on a shared bridge network:

- Dedicated VPN container handles all PIA auth, WireGuard config, NAT, and
  optional port forwarding DNAT
- Service containers default-route through VPN container (leak-proof by topology)
- Host runs tinyproxy on bridge for PIA API bootstrap before WG is up
- WG interface is still created in host netns and moved into VPN container
  namespace
- Monthly renewal to ensure that connection stays up (PIA allows connections to
  last up to 2 months)
- Drop OpenVPN support entirely

common/network/pia-vpn/service-container.nix

@@ -0,0 +1,68 @@
+{ config, lib, allModules, ... }:
+
+# Generates service containers that route all traffic through the VPN container.
+# Each container gets a static IP on the VPN bridge with default route → VPN container.
+#
+# Uses lazy mapAttrs inside fixed config keys to avoid infinite recursion.
+# (mkMerge + mapAttrsToList at the top level forces eager evaluation of cfg.containers
+# during module structure discovery, which creates a cycle with config evaluation.)
+
+with lib;
+
+let
+  cfg = config.pia-vpn;
+
+  mkContainer = name: ctr: {
+    autoStart = true;
+    ephemeral = true;
+    privateNetwork = true;
+    hostBridge = cfg.bridgeName;
+
+    bindMounts = mapAttrs
+      (_: mount: {
+        hostPath = mount.hostPath;
+        isReadOnly = mount.isReadOnly;
+      })
+      ctr.mounts;
+
+    config = { config, pkgs, lib, ... }: {
+      imports = allModules ++ [ ctr.config ];
+
+      # Static IP with gateway pointing to VPN container
+      networking.useNetworkd = true;
+      systemd.network.enable = true;
+      networking.useDHCP = false;
+
+      systemd.network.networks."20-eth0" = {
+        matchConfig.Name = "eth0";
+        networkConfig = {
+          Address = "${ctr.ip}/${cfg.subnetPrefixLen}";
+          Gateway = cfg.vpnAddress;
+          DNS = [ cfg.vpnAddress ];
+        };
+        linkConfig.RequiredForOnline = "no";
+      };
+
+      # DNS through VPN container (queries go through WG tunnel = no DNS leak)
+      networking.nameservers = [ cfg.vpnAddress ];
+
+      # Trust the bridge interface (host reaches us directly for nginx)
+      networking.firewall.trustedInterfaces = [ "eth0" ];
+
+      # Disable host resolv.conf — we use our own networkd DNS config
+      networking.useHostResolvConf = false;
+    };
+  };
+
+  mkContainerOrdering = name: _ctr: nameValuePair "container@${name}" {
+    after = [ "container@pia-vpn.service" ];
+    requires = [ "container@pia-vpn.service" ];
+    partOf = [ "container@pia-vpn.service" ];
+  };
+in
+{
+  config = mkIf cfg.enable {
+    containers = mapAttrs mkContainer cfg.containers;
+    systemd.services = mapAttrs' mkContainerOrdering cfg.containers;
+  };
+}