Enhance docs: add examples and minor fixes Update multiple documentation files with additional examples and small code tweaks: - FileMediaType.md: add examples for category lookup and upload-category validation. - InstallablePackage.md: add manifest generation example and qualify exception usage. - InstallablePackageRecord.md: update APP_PATH to APPLICATION_PATH in examples, add docblocks/comments for methods, and qualify exception usage in example. - RuntimeExtensionInterface.md: add docblocks to register method and include an AI adapter example (Gemini) showing how to register an AI adapter. - UploadedFile.md: add upload error handling example and checksum usage. These are documentation/example improvements and do not change library behavior.
Introduce RuntimeExtension and installable packages Restructure extension model and docs: add RuntimeExtensionInterface and InstallablePackage/InstallablePackageRecord docs, remove legacy Plugin/PluginBase/PluginInterface docs, and update references across the docs to use Runtime Extensions and Installable Packages. Rename Application::registerPlugin to registerRuntimeExtension and update examples; adjust AdapterRegistry, Integrations, Home, Module, Template, UiRenderer, index, and Upgrade-to-v4 to reflect the new runtime vs installable package distinction. Also add detailed database error mapping notes and upgrader behavior for package/plugin-related migrations.