📝 Docs: Streamline Contributing, Issue, PR and Architecture Documentation

[MrAdder]

Fixes #4550

Summary of Changes

Slims down and aligns the contributing and documentation files with the ongoing refactor initiative.

• CONTRIBUTING.md — Rewrote from the old verbose format into a structured, scannable guide covering contribution scope, issue/PR workflow, architecture expectations, testing requirements, and refactor PR guidelines.
• ISSUE_TEMPLATE.md — Expanded from the minimal two-section original to cover type, problem statement, current/expected behavior, affected areas, verification plan, and additional context. Removed overly technical Architectural Impact checkboxes and Risks & Regressions section (both belong in the PR, not the issue).
• PULL_REQUEST_TEMPLATE.md — Expanded with type of change, verification checklist, manual validation, and risk assessment. Removed the redundant Architecture and Behavior Checklist, Queue and Integration Impact section, and duplicate Related section.
• docs/architecture.md — Slimmed from ~100 lines to ~50. Collapsed verbose controller/service "should/should not" lists into tight paragraphs, removed the DTO-Style Response Shaping and Refactor Delivery Rules sections (both duplicated content already in CONTRIBUTING.md), and tightened all remaining sections.

Type of Change

• Bug fix
• Feature
• Refactor (no intended functional change)
• Documentation
• Chore / maintenance

Verification

• Unit tests added/updated where business logic changed
• Feature/integration tests added/updated where contracts changed
• Test suite run locally

Manual Validation

Reviewed all four files for accuracy, consistency, and alignment with the refactor patterns established in #4545, #4549, #4559, and #4577. No functional code was changed.

Risk Assessment

Documentation-only changes. No risk of regressions.

[Copilot]

Pull request overview

Documentation refresh to streamline contributor workflow guidance and capture the refactor-era architecture/testing standards in a single, scannable set of docs/templates.

Changes:

• Add an architecture guide and link it from the repo README.
• Expand and standardize the issue/PR templates with type, verification, manual validation, and risk prompts.
• Rewrite CONTRIBUTING to clarify scope, workflows, architecture expectations, and testing/refactor guidance.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
readme.md	Adds a link to the architecture guide under Getting Started.
docs/architecture.md	Introduces a concise architecture standards guide (layers, queues/jobs, webhooks, providers, testing).
.github/PULL_REQUEST_TEMPLATE.md	Updates PR template to include change type, verification, manual validation, and risk assessment.
.github/ISSUE_TEMPLATE.md	Expands issue template to capture type, problem statement, current/expected behavior, and verification plan.
.github/CONTRIBUTING.md	Rewrites contributing guide with scope, workflows, architecture/testing expectations, and refactor guidelines.

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