[FEAT]: Developer setup guide and enhanced CONTRIBUTING.md

[kasimlohar]

Description

Enhances the existing CONTRIBUTING.md with developer setup instructions,
testing commands, branch conventions, and project structure overview. Adds a
new comprehensive docs/SETUP.md with cross-platform setup guide, common
error solutions, and architecture overview.

New contributors frequently face setup issues (#77, #184, #191, #204, #224).
This PR consolidates solutions in one place.

Fixes #244

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Documentation-only changes — no code is modified. Verified that:

• All internal links resolve correctly (CODE_OF_CONDUCT.md, docs/SETUP.md, docs/docker.md, docs/db.md)
• All external links are valid (GitHub issues, Ollama, Docker, Python downloads)
• Markdown renders correctly on GitHub

Test Configuration:

• N/A — documentation only

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Copilot]

Pull request overview

Adds a comprehensive developer onboarding guide and expands contribution guidelines to reduce repeated setup issues for new contributors.

Changes:

• Introduces docs/SETUP.md with cross-platform setup steps, test commands, environment variables, and common troubleshooting notes.
• Expands CONTRIBUTING.md with quick-start instructions, testing guidance, branch naming, commit conventions, and a project structure overview.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
docs/SETUP.md	New end-to-end developer setup guide (Docker + local) with troubleshooting and architecture overview.
CONTRIBUTING.md	Enhanced contributor guidance: setup quick starts, testing, branching/commits, and repo structure.

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