Add support for Bru (Bruno’s plain-text API collection format)

[Programmer-RD-AI]

Language name

Bru — the plain-text markup language used by the Bruno API client (github).

URL of example repository

https://github.com/usebruno/bruno

Most popular extensions

.bru (github.com).

Why this matters:
Bruno stores API collections as human-readable .bru files for Git-based collaboration, but without Linguist support those files never get highlighted or indexed by language filters. Adding a Bru grammar would improve discoverability and developer ergonomics for Bruno users.