Size the DM screen with dvh so the composer stays on screen in a browser tab

[eldrgeek]

Symptom: in Chrome on a Pixel, the DM composer is off the bottom of the screen and unreachable. Installing the app to the home screen fixes it. That asymmetry is the whole diagnosis.

Cause: 100vh is the large viewport — the height with the URL bar retracted. In a browser tab with the URL bar actually showing, the visible area is ~56px shorter, so body.dm-screen-active .main-content runs past the bottom of the screen. The composer is the last item in that flex column, so it's what goes over the edge, and overflow: hidden means there's no scrolling to it. In standalone display mode there's no URL bar, so 100vh already equals the visible height — which is why it only reproduces in a tab.

Group chat mostly escapes this because layoutChatInputBar() re-pins .chat-input-bar from visualViewport measurements. The DM screen has no equivalent.

Fix: dvh, which tracks the viewport as browser chrome shows and hides. Both rules keep the vh line first as a fallback for older engines — the same pattern .globe-viz-wrap.expanded already uses:

height: calc(100vh - 180px);
height: calc(100dvh - 180px);

Two rules needed it: the base rule and the ≤480px override, which is the one that actually applies on a phone.

Verified on a Pixel in Chrome: composer unreachable before, fully visible after. 7 lines, CSS only.

Worth noting there are two other bare 100vh rules (styles.css lines 33 and 388) that may want the same treatment — I left them alone since they're min-height and I couldn't reproduce a problem with them.

[eldrgeek]

If you want to see this on your own device before merging, here's a live repro that replicates the DM shell — an 80px fixed header, a viewport-sized flex column with overflow: hidden, and the composer as the last static item:

https://mw-safe-area-probe.netlify.app

Tap the vh/dvh button in the header to switch between the two. In vh mode with the URL bar showing, the readout prints how many pixels 100vh overflows the visible area — that number is exactly how far the composer is pushed off screen. In dvh mode it comes back.

Then add it to your home screen and reopen: in standalone mode there's no URL bar, so both modes look correct. That asymmetry is what made the diagnosis obvious.

(Scratch page of mine, not part of the PR — it'll go away once this is settled.)