docs: complete documentation refactoring and structure optimization

This commit finalizes the documentation improvement plan by:
- Centralizing reference material in README.md.
- Creating a dedicated Technical Maintenance guide (docs/howtos/maintenance.md).
- Creating a categorized Sample Queries & Mutations overview (docs/queries/README.md).
- Eliminating redundant information across the doc set (DRY principle).
- Optimizing cross-references between reference documentation and the Cookbook.
- Updating the improvement plan to reflect all tasks as completed.

docs/queries/README.md

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+# Sample Queries & Mutations
+
+This directory contains practical examples of GraphQL operations for the Zabbix GraphQL API. You can use these as templates for your own automation or integration tasks.
+
+## 📁 Available Samples
+
+### 🖥️ Hosts
+- [Query All Hosts](./sample_all_hosts_query.graphql): Retrieve basic host information and inventory.
+- [Import Hosts](./sample_import_hosts_mutation.graphql): Create or update multiple hosts with tags and group assignments.
+- [Query All Devices](./sample_all_devices_query.graphql): Query specialized devices using the `allDevices` query.
+
+### 📄 Templates
+- [Query Templates](./sample_templates_query.graphql): List available templates and their items.
+- [Import Templates](./sample_import_templates_mutation.graphql): Create or update complex templates with item definitions and preprocessing.
+- [Import Distance Tracker Template](./sample_import_distance_tracker_template.graphql): Example of importing a template for a schema extension.
+- [Delete Templates](./sample_delete_templates_mutation.graphql): Remove templates by ID or name pattern.
+
+### 📂 Template Groups
+- [Import Host Template Groups](./sample_import_host_template_groups_mutation.graphql): Create groups specifically for host templates.
+- [Import Permissions Template Groups](./sample_import_permissions_template_groups_mutation.graphql): Create groups for the permission system.
+- [Delete Template Groups](./sample_delete_template_groups_mutation.graphql): Remove template groups by ID or name pattern.
+
+### 🔐 User Rights
+- [Export User Rights](./sample_export_user_rights_query.graphql): Export existing user roles and groups for auditing or migration.
+- [Import User Rights](./sample_import_user_rights_mutation.graphql): Provision user roles and group permissions at scale.
+
+## 🍳 Related Recipes
+For step-by-step guides on how to use these operations in common scenarios, see the [Cookbook](../howtos/cookbook.md).