add comprehensive documentation (#9537)

docs/misc/install.func/INSTALL_FUNC_USAGE_EXAMPLES.md

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+# install.func Usage Examples
+
+Practical examples for using install.func functions in application installation scripts.
+
+## Basic Examples
+
+### Example 1: Minimal Setup
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+setting_up_container
+network_check
+update_os
+
+# ... application installation ...
+
+motd_ssh
+customize
+cleanup_lxc
+```
+
+### Example 2: With Error Handling
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+catch_errors
+setting_up_container
+
+if ! network_check; then
+  msg_error "Network failed"
+  exit 1
+fi
+
+if ! update_os; then
+  msg_error "OS update failed"
+  exit 1
+fi
+
+# ... continue ...
+```
+
+---
+
+## Production Examples
+
+### Example 3: Full Application Installation
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+catch_errors
+setting_up_container
+network_check
+update_os
+
+msg_info "Installing application"
+# ... install steps ...
+msg_ok "Application installed"
+
+motd_ssh
+customize
+cleanup_lxc
+```
+
+### Example 4: With IPv6 Support
+
+```bash
+#!/usr/bin/env bash
+source /dev/stdin <<<"$FUNCTIONS_FILE_PATH"
+
+catch_errors
+setting_up_container
+verb_ip6
+network_check
+update_os
+
+# ... application installation ...
+
+motd_ssh
+customize
+cleanup_lxc
+```
+
+---
+
+**Last Updated**: December 2025
+**Examples**: Basic and production patterns
+**All examples production-ready**