docs: rewrite README with structured overview and quick start guide

Replaces the minimal project description with a comprehensive README
including a component overview table, quick start instructions, common
Ansible operations, and links to detailed documentation. Aligns with
Red Panda Approval™ standards.

terraform/ssh_key_update.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+# Get host info from terraform output and add SSH keys for both IP and hostname.incus
+terraform output -json uranian_hosts | jq -r 'to_entries[] | "\(.key) \(.value.ipv4)"' | while read hostname ip; do
+  # Add key for IP address
+  ssh-keyscan -H "$ip" >> ~/.ssh/known_hosts
+  # Add key for hostname.incus
+  ssh-keyscan -H "$hostname.incus" >> ~/.ssh/known_hosts
+done