STOP is at least 56 px tall and red on touch, and the stopped banner spans the full width #128

Part of #91. Main already has one [data-stop] that fires on pointerdown, and resume already asks for a second tap; pull #104 found these two gaps.

Done:

• [ ] In Software/so101/src/viewer.html, the STOP button's min-height is >= 56 px (it was 52 px), and it stays red.
• [ ] While stopped, #banner.stop spans the full viewport width, not a centred box.
• [ ] src/server.test.ts asserts both from the served page.
• [ ] Branch from current main (044b88b or later). The whole bun --cwd Software/so101 test passes, not only stop.test.ts: pull #104's check went red on the test step. If a test fails without the change too, say which test and why in the pull.