docs(pt): translate handbook-v2/Narrowing

[guuszz]

Summary

Adds the Brazilian Portuguese translation of Narrowing from the TypeScript v2 Handbook, into docs/documentation/pt/handbook-v2/.

This continues the handbook-v2 PT-BR effort (#247 Understanding Errors, #248 The Handbook, #249 Basics, #250 Everyday Types). Narrowing is page #4 in the reading order and one of the most important pages in the whole handbook — it covers typeof guards, truthiness, equality, the in operator, instanceof, type predicates, discriminated unions, never and exhaustiveness checking.

Translation choices

• Followed the established pt/ frontmatter convention: translated title and oneline, adapted permalink to /pt/docs/handbook/2/narrowing.html.
• Preserved every code sample verbatim — all 8 @errors directive lines (codes verified identical to EN), every // ---cut--- (12 of them), and all 26 positional query markers (// ^?) byte-for-byte, so the interactive type-display examples still render.
• Kept the special twoslash/markdown pragmas: {class: "do-not-do-this"}, <!-- prettier-ignore --> and <!-- TODO -->.
• Translated only the explanatory comments inside code blocks (e.g. // DON'T DO THIS! / KEEP READING → // NÃO FAÇA ISSO! / CONTINUE LENDO, keeping the !!!! alignment); identifiers, strings and sample values left unchanged.
• Kept technical terms with a PT gloss on first use (e.g. guarda de tipo (type guard), estreitamento (narrowing), união discriminada (discriminated union), predicado de tipo (type predicate)).

Source

microsoft/TypeScript-Website @ packages/documentation/copy/en/handbook-v2/Narrowing.md

Testing

Read side-by-side with the EN source; verified code fences (70), ---cut--- count (12), ^? marker count (26) and all @errors codes are identical between EN and PT. Cross-checked terminology against the already-merged pt/ pages and my sibling PRs in this series (#247–#250).