doc: update Docker commands and application URL in contributing guide

[wolgwang1729]

Description

• Updated Docker Compose commands in contributing.md from deprecated docker-compose to modern docker compose syntax:
  • docker compose up -d
  • docker compose down
  • docker compose down -v
• Updated local development URL references from http://localhost:3000 to http://localhost:5000 to match the project dev script (next dev -p 5000).
• Improved environment setup instructions by adding a template-based flow:
  • Added cp env.example .env as the primary setup path.
  • Kept manual .env creation instructions as a fallback.

Impact:

• Prevents zsh: command not found: docker-compose errors for contributors using newer Docker installations.
• Aligns docs with the actual runtime port, reducing onboarding confusion.
• Makes initial setup faster and less error-prone by encouraging use of env.example.

Resolved or fixed issue

none

Screenshots (if applicable)

N/A (documentation-only change; no UI updates)

Affirmation

• My code follows the CONTRIBUTING.md guidelines

[vercel]

@wolgwang1729 is attempting to deploy a commit to the shopstr-eng Team on Vercel.

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[Copilot]

Pull request overview

Note

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

Updates the contributing guide to reflect current Docker Compose CLI usage and the app’s actual local development URL/port, while streamlining environment setup.

Changes:

• Replaced deprecated docker-compose commands with docker compose.
• Updated localhost URL references from port 3000 to 5000.
• Added a template-based .env setup path (cp env.example .env) with a manual fallback.

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