Add entity context documentation to customization and add-memories pages, remove nav icons from Developer Platform, fix install.md parsing error
Changes:
- Remove icons from Developer Platform subheadings (Getting Started, Concepts, Using supermemory, Connectors and sync, Migration Guides)
- Add Entity Context section to customization page with usage example and accordion for advanced API
- Add entityContext parameter to add-memories Parameters table and examples accordion
- Fix MDX parsing error in install.md (wrap curly braces in backticks)