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/casdoor/remove.yml

@@ -0,0 +1,75 @@
+---
+# -----------------------------------------------------------------------------
+# Casdoor Removal Playbook
+# -----------------------------------------------------------------------------
+# Removes Casdoor SSO including:
+# - Docker containers and volumes
+# - Configuration files
+# - PostgreSQL data directory
+# - Service user and group
+#
+# WARNING: This will permanently delete all Casdoor data including the database!
+# -----------------------------------------------------------------------------
+
+- name: Remove Casdoor
+  hosts: ubuntu
+  tasks:
+    - name: Check if host has casdoor service
+      ansible.builtin.set_fact:
+        has_casdoor_service: "{{ 'casdoor' in services | default([]) }}"
+
+    - name: Skip hosts without casdoor service
+      ansible.builtin.meta: end_host
+      when: not has_casdoor_service
+
+    # -------------------------------------------------------------------------
+    # Stop and Remove Docker Services
+    # -------------------------------------------------------------------------
+
+    - name: Check if docker-compose.yml exists
+      become: true
+      ansible.builtin.stat:
+        path: "{{ casdoor_directory }}/docker-compose.yml"
+      register: compose_file
+
+    - name: Stop and remove Casdoor containers
+      become: true
+      community.docker.docker_compose_v2:
+        project_src: "{{ casdoor_directory }}"
+        state: absent
+        remove_volumes: true
+      when: compose_file.stat.exists
+
+    # -------------------------------------------------------------------------
+    # Remove Data Directory
+    # -------------------------------------------------------------------------
+
+    - name: Remove casdoor directory and all data
+      become: true
+      ansible.builtin.file:
+        path: "{{ casdoor_directory }}"
+        state: absent
+
+    # -------------------------------------------------------------------------
+    # Remove User and Group
+    # -------------------------------------------------------------------------
+
+    - name: Remove ponos from casdoor group
+      become: true
+      ansible.builtin.command:
+        cmd: gpasswd -d ponos {{ casdoor_group }}
+      register: gpasswd_result
+      changed_when: gpasswd_result.rc == 0
+      failed_when: false
+
+    - name: Remove casdoor user
+      become: true
+      ansible.builtin.user:
+        name: "{{ casdoor_user }}"
+        state: absent
+
+    - name: Remove casdoor group
+      become: true
+      ansible.builtin.group:
+        name: "{{ casdoor_group }}"
+        state: absent