docs: clarify README scope and fix development instructions

[altaskur]

The current documentation has some inconsistencies and scope overlap that can be confusing for new contributors.

Main issues identified:

• The README includes internal development and usage details (e.g. keyboard shortcuts, detailed workflows) that would be better suited for dedicated docs.
• Development instructions were unclear regarding the recommended command to work on the project (npm run dev vs npm start).
• Some information is duplicated across README and contributing-related files, increasing the risk of them getting out of sync.

Goal of this issue:

• Simplify and refocus the README as a project entry point.
• Clarify the recommended development workflow.
• Reduce duplication by linking to dedicated contribution and technical documents.

This is a documentation-only task, no functional changes involved.