docs: add architecture overview documentation

[srinidhi-2006-bit]

Summary

Added architecture overview documentation with a Mermaid-based system architecture diagram explaining DevTrack’s frontend, API layer, database, and external integrations.

Closes #1038

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

Changes Made

• Added docs/architecture.md
• Added Mermaid system architecture diagram
• Documented frontend, API, database, and external service flow
• Added README link to architecture documentation

How to Test

1. Open docs/architecture.md
2. Verify the Mermaid diagram renders correctly
3. Check that all architecture sections display properly
4. Open README.md
5. Verify the Architecture Overview documentation link works correctly

Screenshots (if UI change)

N/A

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

[vercel]

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[srinidhi-2006-bit]

Thanks for reviewing the PR.

The failing Playwright smoke test appears unrelated to this documentation-only change, since build, lint, and type-check checks are all passing successfully.

This PR only adds architecture documentation and README references without modifying application logic or E2E-related functionality.

[Priyanshu-byte-coder]

Playwright smoke tests are failing on this PR. Check the CI logs, fix failing tests, then push an update. Cannot merge while tests are red.

[Priyanshu-byte-coder]

Playwright smoke tests are failing on this PR. Please check the E2E test failures and fix them before merging.

[srinidhi-2006-bit]

I investigated the failing Playwright smoke tests locally.

The failures appear unrelated to this documentation-only PR because this PR only adds:

• architecture documentation
• Mermaid system diagram
• README references

No application logic, routing, authentication flow, or E2E-related functionality was modified.

I verified locally that:

• npm run lint passes
• npm run type-check passes
• npm run build passes

The current Playwright failures are caused by existing repo-wide E2E assertions expecting outdated UI/routes/components rather than changes introduced in this PR.

[Priyanshu-byte-coder]

CI is failing on this PR. Please fix the failing checks before this can be merged.

[srinidhi-2006-bit]

done