[DOC] all: Reorganize and consolidate project documentation

- Create .github/copilot-instructions.md with global development guidelines
- Add comprehensive README.md at project root with quick start guide
- Create docs/ directory for technical documentation
- Move installation and linter docs to docs/
- Add docs/TRANSLATIONS.md with complete translation system guide
- Create README.md for OCA modified addons (product_origin, product_get_price_helper, product_main_seller)
- Document translation best practices (no _() in field definitions)
- Add references between all documentation files
- Clean up project root by moving technical docs to docs/

All documentation now properly references addon-specific READMEs for detailed architecture and implementation.

product_origin/README.md

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+# Product Origin
+
+## Summary
+
+Adds an origin field to products to track where they come from (geographic origin).
+
+## Features
+
+- **Origin Field**: Adds a text field to store the product's origin
+- **Visible in Views**: Shows in both product template and product variant forms
+- **Simple Implementation**: Extends core product models
+
+## Technical Details
+
+### Models Extended
+
+- `product.template`: Main product template
+- `product.product`: Product variants
+
+### Fields Added
+
+- `origin` (Char): Text field for product origin
+
+### Views Modified
+
+- Product Template Form
+- Product Variant Form
+
+## Dependencies
+
+- `product` (Odoo core)
+
+## Installation
+
+```bash
+docker-compose exec odoo odoo -d odoo -u product_origin --stop-after-init
+```
+
+## Usage
+
+1. Open a product form (Products > Products > [Product])
+2. Find the "Origin" field
+3. Enter the geographic origin (e.g., "Spain", "France", "Local")
+
+## OCA Source
+
+- **Repository**: [product-attribute](https://github.com/OCA/product-attribute)
+- **Original Authors**: ACSONE SA/NV, GRAP
+- **License**: AGPL-3
+
+## Modifications for Kidekoop
+
+None - Used as-is from OCA.
+
+## Translations
+
+- ✅ Spanish (es)
+- ✅ Euskera (eu)
+
+Located in `i18n/` directory.
+
+---
+
+**Version**: 18.0.1.0.0
+**License**: AGPL-3