Docs: Add Next.js Glossary

[delbaoliveira]

Add next.js glossary so we can reference concepts in guides without having to re-explain them. Guides should be succint, like a skill :)

Closes: https://linear.app/vercel/issue/DOC-5574/nextjs-glossary

[github-actions]

All broken links are now fixed, thank you!

[icyJoseph]

I had a bunch of terms on my version, pasting here for completeness. We do mention these in the docs 10+ times:

"use client" directive: A special statement that marks the boundary between server and client code. It must be placed at the top of a file, before any imports or other code. It indicates that React Components, helper functions, variable declarations, and all imported dependencies should be included in the client bundle. Learn more about this directive.

Module Graphs: A graph of file dependencies in your app. Each file (module) is a node, and import/export relationships form the edges. Next.js analyzes this graph to determine optimal bundling and code-splitting strategies.

Client Bundles: JavaScript bundles sent to the browser. Next.js splits these automatically based on the module graph to reduce initial payload size and load only the necessary code for each page.

Catch-all segments: Dynamic route segments that can match multiple URL parts using the [...folder]/page.js syntax. These segments capture all remaining URL segments and are useful for implementing features like documentation sites or file browsers.

Private folders: Folders prefixed with an underscore (e.g., _components) that are excluded from the routing system. These folders are used for code organization and shared utilities without creating accessible routes.

Static assets: Files such as images, fonts, videos, and other media that are served directly without processing. Static assets are typically stored in the public directory and referenced by their relative paths.

Import aliases: Custom path mappings that provide shorthand references for frequently used directories. Import aliases reduce the complexity of relative imports and make code more readable and maintainable.