docs(blog): building on JavaScript, not around it

[vivek7405]

New engineering blog post prompted by a re-read of You Don't Know JS.

Maps each language pillar the book covers onto a WebJs design decision:

• Modules / closures: native ESM as the framework's real graph; module-scope vs instance-scope signals.
• Objects & classes: reactive properties are prototype accessors via Object.defineProperty; the class-field-clobbers-accessor footgun and the lint that catches it.
• Types & grammar: the wire serializer round-trips BigInt, Map, Set, Symbol.for, and cycles; local symbols and functions are rejected, with the reason the book gives.
• Sync & async: async render() and async-generator streaming over the plain iteration protocol.

Serializer claims were exercised against the live runtime before publishing. Voice, front matter, de-dup, and all punctuation/brand rules checked per the blog skill.