docs: revisit wording & style for liquidjs.com (#906)

* docs: polish theme, playground, and reference pages

Improve readability of the docs site with updated light/dark tokens, shared
code-block styling, and playground editors that follow system color scheme.
Skip CookieHub on localhost, serve the browser bundle from theme source, and
use backtick titles on filter/tag reference pages for consistent navigation.

Co-authored-by: Cursor <[email protected]>

* docs: highlight npx in bash blocks and polish English copy

Use Prism insertBefore for CLI commands like npx, tighten tutorial and reference wording, and keep YAML titles free of backticks so sidebar and page headings stay correct.

Co-authored-by: Cursor <[email protected]>

* docs: restore lowercase filter and tag titles

Titles should match actual filter/tag identifiers (e.g. abs, append), not capitalized English labels.

Co-authored-by: Cursor <[email protected]>

---------

Co-authored-by: Cursor <[email protected]>

docs/source/tutorials/sync-and-async.md

@@ -2,11 +2,11 @@
 title: Sync and Async
 ---
 
-LiquidJS supports both sync and async evaluate, and can be used with Promises. To reuse the same set of tag/filter implementations in both sync and async, LiquidJS tags are implemented as generators.
+LiquidJS supports both synchronous and asynchronous evaluation, and can be used with Promises. To reuse the same set of tag/filter implementations in both sync and async modes, LiquidJS tags are implemented as generators.
 
 ## Sync and Async API
 
-All major methods on [Liquid][Liquid] supports both sync and async. These methods return Promises:
+All major methods on [Liquid][Liquid] support both sync and async. These methods return Promises:
 
 - `render()`
 - `renderFile()`
@@ -44,11 +44,11 @@ engine.registerTag('upper', class UpperTag extends Tag {
 })
 ```
 
-All builtin tags are implemented this way and safe to use in both sync and async (I'll call it *sync-compatible*). To make your custom tag *sync-compatible*, you'll need to:
+All built-in tags are implemented this way and are safe to use in both sync and async modes (I'll call it *sync-compatible*). To make your custom tag *sync-compatible*, you'll need to:
 
 - declare render function as `* render()`, in which
 - do not directly `return <Promise>`, and
-- do not call any APIs that returns a Promise.
+- do not call any APIs that return a Promise.
 
 ## Call APIs that return a Promise
 
@@ -92,7 +92,7 @@ engine.registerTag('upper', class UpperTag extends Tag {
 
 ## Async only Tags
 
-If your tag is intend to be used only asynchronously, it can be declared as `async render()` so you can use `await` in its implementation directly:
+If your tag is intended to be used only asynchronously, it can be declared as `async render()` so you can use `await` in its implementation directly:
 
 ```typescript
 import { toPromise, TagToken, Context, Emitter, TopLevelToken, Value, Tag, Liquid } from 'liquidjs'