docs: restructure and expand documentation with new guides and pages

- Add getting-started section (quickstart, concepts, project structure, complete user example)
- Add new pages: FAQ, security, 404, CODE_OF_CONDUCT
- Add examples: dependency injection, observability, testing strategy
- Remove deprecated concepts.md and bdd_testing.md
- Update adapter examples, contributing guide, and index page
- Update mkdocs.yml navigation to reflect new structure

Author: HosseinNejatiJavaremi

docs/404.md

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+---
+title: Page Not Found
+description: The requested page could not be found. Navigate to the ArchiPy documentation home.
+---
+
+# Page Not Found
+
+The page you were looking for does not exist.
+
+It may have been moved, renamed, or deleted.
+
+## Find What You Need
+
+- [Get Started](index.md) — overview and quick example
+- [Installation](installation.md) — install ArchiPy and optional extras
+- [Quickstart](getting-started/quickstart.md) — five-minute step-by-step guide
+- [Concepts](getting-started/concepts.md) — Clean Architecture layers and import rules
+- [Tutorials](examples/index.md) — guides for every adapter and helper
+- [API Reference](api_reference/index.md) — full reference for all public classes
+- [FAQ](faq.md) — frequently asked questions
+
+!!! tip "Search the docs"
+Use the search bar at the top of the page to find any topic instantly.

docs/CODE_OF_CONDUCT.md

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+---
+title: Code of Conduct
+description: ArchiPy community standards for respectful and inclusive collaboration.
+---
+
+# Code of Conduct
+
+## Our Pledge
+
+We as members, contributors, and leaders pledge to make participation in the ArchiPy community a harassment-free
+experience for everyone, regardless of age, body size, visible or invisible disability, ethnicity, sex
+characteristics, gender identity and expression, level of experience, education, socioeconomic status,
+nationality, personal appearance, race, caste, colour, religion, or sexual identity and orientation.
+
+We pledge to act and interact in ways that contribute to an open, welcoming, diverse, inclusive, and healthy
+community.
+
+## Our Standards
+
+**Examples of behaviour that contributes to a positive environment:**
+
+- Demonstrating empathy and kindness toward other people
+- Being respectful of differing opinions, viewpoints, and experiences
+- Giving and gracefully accepting constructive feedback
+- Accepting responsibility and apologising to those affected by our mistakes
+- Focusing on what is best not just for us as individuals, but for the overall community
+
+**Examples of unacceptable behaviour:**
+
+- The use of sexualised language or imagery, and sexual attention or advances of any kind
+- Trolling, insulting or derogatory comments, and personal or political attacks
+- Public or private harassment
+- Publishing others' private information without explicit permission
+- Other conduct which could reasonably be considered inappropriate in a professional setting
+
+## Enforcement Responsibilities
+
+Community leaders are responsible for clarifying and enforcing our standards of acceptable behaviour
+and will take appropriate and fair corrective action in response to any behaviour that they deem
+inappropriate, threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies within all community spaces, and also applies when an individual is officially
+representing the community in public spaces.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behaviour may be reported to the community leaders
+via the [GitHub repository](https://github.com/SyntaxArc/ArchiPy). All complaints will be reviewed and
+investigated promptly and fairly.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant](https://www.contributor-covenant.org/),
+version 2.1, available at
+[https://www.contributor-covenant.org/version/2/1/code_of_conduct.html](https://www.contributor-covenant.org/version/2/1/code_of_conduct.html).
+
+## See Also
+
+- [Contributing](contributing.md) — how to contribute code, docs, and bug reports