docs: add comprehensive installation and usage docs to all package READMEs

[Copilot]

Each package README contained only a single sentence pointing to the website. The root README lacked per-package detail. This PR expands all four to be self-contained references.

Root README.md

• Replaces flat "Installation" section with a Packages section
• Each package gets its own description, install snippet, usage example, and a list of available effects/components/elements
• Fixes a typo: <bx-slider-controls> → <bs-slider-controls> (with correct closing tag)

packages/slider/README.md

• Installation via NPM and CDN
• Usage with HTML structure + factory function call
• BoxSliderOptions reference table (all 8 options)
• All four effects (createCarouselSlider, createCubeSlider, createFadeSlider, createTileSlider) with their effect-specific options
• Event listener examples and BoxSlider instance API (next, prev, skipTo, play, pause, reset, destroy, activeIndex, length, getOption)

packages/react/README.md

• React 19+ requirement + installation
• All five components with props tables: CarouselSlider, CubeSlider, FadeSlider, TileSlider, SliderControls
• Common slider props table shared across all components
• Event handler props (onBefore, onAfter, onPlay, onPause, …) with sliderRef usage example

packages/components/README.md

• Installation via NPM and CDN
• All five custom elements with attribute tables: <bs-carousel>, <bs-cube>, <bs-fade>, <bs-tile>, <bs-slider-controls>
• unstyled attribute for opting out of built-in control styles
• Common attributes table and custom events reference

<!-- components example -->
<bs-slider-controls>
  <bs-carousel timing-function="ease-in-out">
    <div>Slide one</div>
    <div>Slide two</div>
  </bs-carousel>
</bs-slider-controls>

// React example with event handlers and ref access
const sliderRef = useRef<BoxSlider>(null)

<CarouselSlider
  sliderRef={sliderRef}
  onBefore={({ currentIndex, nextIndex }) => …}
  onAfter={({ currentIndex }) => …}
>
  …
</CarouselSlider>

Original prompt

Update package readme files with a more comprehensive description of how to install and use the library and components. Also update the root readme with more details about the individual packages

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