Pairs with NativePHP/mobile-air#252 / NativePHP/mobile-air#348, which makes Route::native()->middleware() run on every navigation rather than only on cold start.

New page at the-basics/middleware (order 153, right after Routing), plus a pointer to it from the Routing page's "Registering routes" section.

Covers:

• ->middleware() and route groups, both of which now work unchanged
• why native middleware is different — the app enters its runloop once, so only the launch screen arrives as an HTTP request
• what the synthesized request does and does not carry. It has the live session, user resolver, cookies and server bag; it has no body, query string, files, real headers or client IP, and the method is always GET. This is the deliberate trade-off in the implementation and the main thing users need to know before relying on it
• which request-lifecycle middleware is skipped, and ScreenGuard::skip() for opting your own out
• how a refusal maps onto native navigation, plus the two guarantees (a refused screen never mounts; guards fail closed)
• why Native::visit() exercises a guard and Native::test() deliberately doesn't — the distinction that let this bug hide from an otherwise thorough suite

Should land with (or just after) the mobile-air PR, since it documents behavior that doesn't exist yet.