Add Docker setup, .env.example, updated .gitignore/CHANGELOG and ADRs 004-007 + arc42 template

docs/architecture/templates/arc42-template-EN.md

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+---
+date: July 2025
+title: "![arc42](images/arc42-logo.png) Template"
+---
+
+# 
+
+**About arc42**
+
+arc42, the template for documentation of software and system
+architecture.
+
+Template Version 9.0-EN. (based upon AsciiDoc version), July 2025
+
+Created, maintained and © by Dr. Peter Hruschka, Dr. Gernot Starke and
+contributors. See <https://arc42.org>.
+
+# Introduction and Goals {#section-introduction-and-goals}
+
+## Requirements Overview {#_requirements_overview}
+
+## Quality Goals {#_quality_goals}
+
+## Stakeholders {#_stakeholders}
+
++-------------+---------------------------+---------------------------+
+| Role/Name   | Contact                   | Expectations              |
++=============+===========================+===========================+
+| *           | *\<Contact-1\>*           | *\<Expectation-1\>*       |
+| \<Role-1\>* |                           |                           |
++-------------+---------------------------+---------------------------+
+| *           | *\<Contact-2\>*           | *\<Expectation-2\>*       |
+| \<Role-2\>* |                           |                           |
++-------------+---------------------------+---------------------------+
+
+# Architecture Constraints {#section-architecture-constraints}
+
+# Context and Scope {#section-context-and-scope}
+
+## Business Context {#_business_context}
+
+**\<Diagram or Table\>**
+
+**\<optionally: Explanation of external domain interfaces\>**
+
+## Technical Context {#_technical_context}
+
+**\<Diagram or Table\>**
+
+**\<optionally: Explanation of technical interfaces\>**
+
+**\<Mapping Input/Output to Channels\>**
+
+# Solution Strategy {#section-solution-strategy}
+
+# Building Block View {#section-building-block-view}
+
+## Whitebox Overall System {#_whitebox_overall_system}
+
+***\<Overview Diagram\>***
+
+Motivation
+
+:   *\<text explanation\>*
+
+Contained Building Blocks
+
+:   *\<Description of contained building block (black boxes)\>*
+
+Important Interfaces
+
+:   *\<Description of important interfaces\>*
+
+### \<Name black box 1\> {#_name_black_box_1}
+
+*\<Purpose/Responsibility\>*
+
+*\<Interface(s)\>*
+
+*\<(Optional) Quality/Performance Characteristics\>*
+
+*\<(Optional) Directory/File Location\>*
+
+*\<(Optional) Fulfilled Requirements\>*
+
+*\<(optional) Open Issues/Problems/Risks\>*
+
+### \<Name black box 2\> {#_name_black_box_2}
+
+*\<black box template\>*
+
+### \<Name black box n\> {#_name_black_box_n}
+
+*\<black box template\>*
+
+### \<Name interface 1\> {#_name_interface_1}
+
+...​
+
+### \<Name interface m\> {#_name_interface_m}
+
+## Level 2 {#_level_2}
+
+### White Box *\<building block 1\>* {#_white_box_building_block_1}
+
+*\<white box template\>*
+
+### White Box *\<building block 2\>* {#_white_box_building_block_2}
+
+*\<white box template\>*
+
+...​
+
+### White Box *\<building block m\>* {#_white_box_building_block_m}
+
+*\<white box template\>*
+
+## Level 3 {#_level_3}
+
+### White Box \<\_building block x.1\_\> {#_white_box_building_block_x_1}
+
+*\<white box template\>*
+
+### White Box \<\_building block x.2\_\> {#_white_box_building_block_x_2}
+
+*\<white box template\>*
+
+### White Box \<\_building block y.1\_\> {#_white_box_building_block_y_1}
+
+*\<white box template\>*
+
+# Runtime View {#section-runtime-view}
+
+## \<Runtime Scenario 1\> {#_runtime_scenario_1}
+
+-   *\<insert runtime diagram or textual description of the scenario\>*
+
+-   *\<insert description of the notable aspects of the interactions
+    between the building block instances depicted in this diagram.\>*
+
+## \<Runtime Scenario 2\> {#_runtime_scenario_2}
+
+## ...​
+
+## \<Runtime Scenario n\> {#_runtime_scenario_n}
+
+# Deployment View {#section-deployment-view}
+
+## Infrastructure Level 1 {#_infrastructure_level_1}
+
+***\<Overview Diagram\>***
+
+Motivation
+
+:   *\<explanation in text form\>*
+
+Quality and/or Performance Features
+
+:   *\<explanation in text form\>*
+
+Mapping of Building Blocks to Infrastructure
+
+:   *\<description of the mapping\>*
+
+## Infrastructure Level 2 {#_infrastructure_level_2}
+
+### *\<Infrastructure Element 1\>* {#_infrastructure_element_1}
+
+*\<diagram + explanation\>*
+
+### *\<Infrastructure Element 2\>* {#_infrastructure_element_2}
+
+*\<diagram + explanation\>*
+
+...​
+
+### *\<Infrastructure Element n\>* {#_infrastructure_element_n}
+
+*\<diagram + explanation\>*
+
+# Cross-cutting Concepts {#section-concepts}
+
+## *\<Concept 1\>* {#_concept_1}
+
+*\<explanation\>*
+
+## *\<Concept 2\>* {#_concept_2}
+
+*\<explanation\>*
+
+...​
+
+## *\<Concept n\>* {#_concept_n}
+
+*\<explanation\>*
+
+# Architecture Decisions {#section-design-decisions}
+
+# Quality Requirements {#section-quality-scenarios}
+
+## Quality Requirements Overview {#_quality_requirements_overview}
+
+## Quality Scenarios {#_quality_scenarios}
+
+# Risks and Technical Debts {#section-technical-risks}
+
+# Glossary {#section-glossary}
+
++----------------------+-----------------------------------------------+
+| Term                 | Definition                                    |
++======================+===============================================+
+| *\<Term-1\>*         | *\<definition-1\>*                            |
++----------------------+-----------------------------------------------+
+| *\<Term-2\>*         | *\<definition-2\>*                            |
++----------------------+-----------------------------------------------+