Update backend development architecture docs

[officialasishkumar]

Fix #11403

Describe changes proposed in this pull request:

• Update the backend code organization documentation for the current single-module Spring Boot backend.
• Document the package-level application, domain, infrastructure, legacy, shared, resource, and test boundaries.
• Refresh backend development guidance for the current master/v7 ClickHouse-only codebase.
• Update the architecture overview language so it no longer describes the old multi-module/importer-oriented backend layout.

Checks

• The commits in the pull request have descriptive commit messages, including a short title and a paragraph describing the change.
• Documentation-only change validated with git diff --check.
• No application logic based on clinical attributes is added.
• Apply the relevant release-drafter label for this pull request: documentation.
• Screenshots are not applicable for this documentation update.
• Reviewers can be routed through the normal maintainer triage process.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates backend developer documentation to reflect the v7 single-module Spring Boot architecture with clean-architecture package layout, replacing outdated multi-module Maven guidance.

Changes:

• Rewrites Backend-Development-Guidelines.md with current architecture, REST, domain, data access, testing, and configuration guidance.
• Rewrites Backend-Code-Organization.md to describe the application/domain/infrastructure/legacy package layout and ClickHouse-based runtime.
• Updates Architecture-Overview.md to remove references to the old multi-module Maven structure.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
docs/development/Backend-Development-Guidelines.md	Replaces deprecated guidelines with v7-oriented guidance covering architecture, REST, domain, data access, legacy, tests, configuration, and code style.
docs/development/Backend-Code-Organization.md	Replaces multi-module Maven description with a package-based clean architecture overview and feature-addition workflow.
docs/Architecture-Overview.md	Updates backend description to reflect a single-module Spring Boot application.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud