fix(mobile): the drawer no longer pushes the page sideways

The task drawer was `width: 100vw`. A viewport unit includes the scrollbar
gutter and a percentage does not, so the drawer came out a few pixels wider
than the page it was pinned to and the whole document could be shoved
sideways. It is `100%` now, and at phone width it is stated as four insets
instead — a box defined by the viewport's own edges cannot be a rounding
error wider than it.

The scrolling body gets `min-width: 0` and `overflow-x: hidden` too, so a
pasted URL or a long unbroken word in a comment cannot stretch the flex
column and take the page with it.

Writing the test for that found another one: creating a project from the
sidebar navigated to it and left the drawer covering the screen. Every link
in there closes it on the way out; the form did not, because it calls
`goto` directly. Now it does the same thing for the same reason.

The phone test checks the document cannot be scrolled horizontally, both
with the drawer shut and with it open.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/lib/components/Sidebar.svelte

@@ -18,7 +18,13 @@
 		newName = '';
 		adding = false;
 		const project = await app.createProject(name);
-		if (project) goto(`/projekt/${project.id}`);
+		if (!project) return;
+		// Closes the drawer as well as navigating. On a phone the sidebar is an
+		// overlay, and creating a project moved the page underneath it while leaving
+		// it covering the screen — every link in here closes it, and this makes the
+		// same move for the same reason.
+		onnavigate?.();
+		goto(`/projekt/${project.id}`);
 	}
 
 	async function signOut() {