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/fetch_secrets.yml.vault_example

@@ -0,0 +1,19 @@
+---
+# Example: Ansible Vault Implementation
+# Replace fetch_secrets.yml with this file if using Ansible Vault
+#
+# This implementation does nothing because vault variables are automatically
+# loaded from inventory/group_vars/all/vault.yml when using --ask-vault-pass
+#
+# Usage:
+#   cp fetch_secrets.yml.vault_example fetch_secrets.yml
+
+- name: Fetch Secrets (Ansible Vault)
+  hosts: all
+  gather_facts: false
+  tasks:
+    - name: Verify vault variables are loaded
+      ansible.builtin.debug:
+        msg: "Using Ansible Vault - secrets loaded from vault.yml"
+      run_once: true
+      when: secret_scope is not defined