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.

ansible/inventory/group_vars/all/auth_keys.yml

@@ -0,0 +1,36 @@
+---
+# SSH Authorized Keys Configuration
+# Manages authorized_keys files across all ubuntu hosts
+#
+# Usage:
+#   ansible-playbook ssh_keys.yml
+#
+# To override exclusive mode (remove unlisted keys):
+#   ansible-playbook ssh_keys.yml -e "ssh_exclusive_mode=true"
+
+# When true, removes any keys not in this list (use with caution!)
+ssh_exclusive_mode: false
+
+# List of users and their authorized SSH public keys
+# Each user entry requires:
+#   - name: username (must exist on target hosts)
+#   - keys: list of SSH public key strings
+#
+# Example:
+#   ssh_authorized_users:
+#     - name: robert
+#       keys:
+#         - "ssh-ed25519 AAAAC3Nza... user@host"
+#         - "ssh-rsa AAAAB3Nza... another@host"
+#     - name: deploy
+#       keys:
+#         - "ssh-ed25519 AAAAC3Nza... deploy-key"
+
+ssh_authorized_users:
+  - name: robert
+    keys:
+      - "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIH0xFMMSa1SeMPbX84zJOKWHAT3HtMRuWmNA7GGKr1uw robert@Hercules"
+      - "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBTcpW11Vb3w1Bi77WCAM5K9Q2vz9MW5PdBpiAIXhjn3 robert@Norma"
+  - name: harper
+    keys:
+      - "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOVvIshMkRx1f9m2TTJ1lMHzsaBnuxZdoMFm6hmuzZzo harper@caliban"