fix(web): remove black bezels + better integrate ActivityStatus

[pyorot]

My entire description was deleted so I'll keep it brief I guess.

Fixes #10526

Couldn't test properly cos the headers-already-sent bug broke the video and changed the appearance of the controls but think it's OK.

Tried to right-align the buttons and make ActivityControl as-if a kind of second-row from the bottom, symmetrical to the top row. TODO: It should be first-row from bottom on PhotoViewer but idk how to condition in Svelte macros for PhotoViewer vs VideoViewer appearing.

Tried to also make ActivityControl less obtrusive, so removed the "Say Something" text (because it does not fade out nor disappear if the viewport width is decreased). I left the code in a comment and noted these two conditions for maybe bringing it back, tho it's a bit subjective whether it's useful or not.