Initial cluster config: NixOS flake + k3s + 5 node definitions

- Multi-host flake.nix (3x N97 x86_64 + 2x RPi4 aarch64)
- Shared modules: k3s-cluster, tailscale, meos-gateway
- Node configs: n97-1 (control plane), n97-2/n97-3 (Ollama workers), rpi4-1/rpi4-2 (ARM workers)
- K8s manifests: Forgejo, Postgres (CNPG), Umami, OpenBrain, MeOS Dashboard, MCP servers
- Bootstrap and DB migration scripts
- Migration plan doc (7-day phased rollout)

hardware-rpi4.nix

@@ -0,0 +1,23 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # Raspberry Pi 4 — aarch64 worker node
+  boot = {
+    kernelPackages = pkgs.linuxPackages_rpi4;
+    loader = {
+      grub.enable = false;
+      generic-extlinux-compatible.enable = true;
+    };
+  };
+
+  # ARM-specific performance
+  hardware.enableRedistributableFirmware = true;
+
+  # Local storage
+  systemd.tmpfiles.rules = [
+    "d /data/k3s 0755 root root -"
+  ];
+
+  # RPi 4 throttling protection
+  powerManagement.cpuFreqGovernor = "ondemand";
+}