Add ARCHITECTURE.md documenting internal design and processing flows

[Copilot]

• Create ARCHITECTURE.md explaining ReqStream's architecture
  • Document core data model (Requirement, Section, Requirements)
  • Explain reading and merging requirements workflow
  • Document trace matrix construction and analysis
  • Explain test coverage enforcement mechanism
  • Include architectural diagrams (using markdown)
• Update AGENTS.md to reference ARCHITECTURE.md
• Update .github/agents/*.md files to reference ARCHITECTURE.md
• Run linters and verify changes (all passed)
• Run code review and security scanning (no issues found)
• Add ARCHITECTURE.md to Project Structure tree diagram

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature]: Architecture Documentation</issue_title>
<issue_description>### Problem Statement

An ARCHITECTURE.md file needs to be created which explains the architecture of the ReqStream tool.

Proposed Solution

Create an ARCHITECTURE.md file which explains the working of the ReqStream tool.

Of importance is explaining the process by which ReqStream performs its core functional tasks of:

• Reading and merging requirements
• Constructing a trace matrix and analyzing test results
• Enforcing test coverage

The architectural explanations should make it easy to explain exactly how the tool performs its core function - however if the explanation is complex because the functionality is complex, then consider if there are changes to the implementation which would make the code and corresponding architectural explanations simpler. These changes may be as simple as renaming functions, or possibly altering the execution flow.

Alternatives Considered

No response

Additional Context

It may also be appropriate to add a reference to the ARCHITECTURE.md to the AGENTS.md suggesting the ARCHITECTURE should be reviewed for details on the behavior of the tool.

Additionally it may be appropriate to update some of the GitHub agent files to have them consider the ARCHITECTURE.md in their work.

Priority

Medium - Would improve workflow

Contribution

• I would be willing to submit a PR for this feature

Code of Conduct

• I agree to follow this project's Code of Conduct</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature]: Architecture Documentation #63

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[Malcolmnixon]

Consider adding the ARCHITECTURE.md file to the Project Structure of the AGENTS.md file

[Copilot]

Consider adding the ARCHITECTURE.md file to the Project Structure of the AGENTS.md file

Added ARCHITECTURE.md to the Project Structure tree diagram in commit dfb56d6.