docs(readme): restructure, dedupe layout/config, tighten quickstart

- Move repository setup to top as 6-step quickstart
- Remove duplicate "Module structure requirements" section
- Consolidate scattered configuration into one canonical section
- Collapse detailed tables (gates, inputs/outputs) into <details> blocks
- Merge two release sections into unified "Release control with labels"
- Complete truncated default YAML config
- Standardize code fence languages (yaml, powershell, plaintext)
- Add Contributing/License sections
- Flatten heading hierarchy for improved scanability

No workflow behavior changes. Documentation-only refactor.

Author: MariusStorhaug