Make the back arrow and menu follow one rule

[KadyrovAkram]

Fixes how Vacant chooses between the hamburger menu and the back arrow, plus several Back bugs. One commit per fix.

The rule now

One function, chromeFor(), decides it for every screen:

• Phone: the card and the way keep ☰ in the corner. Every screen below them gets ← in the same corner.
• Desktop: the corner always holds ☰. Back goes in the panel, at the same inset as the room's header, on every pane.
• Way: keeps ☰, and has its own ← on the plate naming the room.

Commits

1. Record the screen underneath on every history entry. pick, browse, about, near, way, card and the picker's replaceState now carry from.
2. Name every Back from the entry it lands on. One backLabel() replaces per-screen strings and roomBackLabel. It fixes the list saying "Back to the card" when opened from a desktop room, and after picking a building from the way.
3. Decide a screen's way out in one function. chromeFor() and paintChrome() replace the decisions in showPane, showAsk, showWay and the per-breakpoint body.rooming CSS. A resize across the breakpoint re-decides.
4. Keep the desktop corner for the menu on every screen. Adds #sheet-back in the panel for list, near, pick, browse and about.
5. Give the way a Back of its own, and name the menu's. #way-back sits on the plate. The menu's Back reads "Back to the question" and is hidden wherever another Back shows.
6. Step back onto the card when Check again loses the way's room. Previously history became question → card → card, and the next Back appeared to do nothing.
7. Land focus on the screen a menu choice opens. Focus used to drop to <body> after the menu hid its own button.
8. Return to the screen underneath instead of stacking a copy. Fixes the list → room → list loop from the desktop menu.
9. Draw the phone's corner arrow the way the menu is drawn. Same 60px target, 40px glyph and position, so the corner no longer jumps 16px from card to room.

Testing

• npm test: 938 pass. The source-pattern tests in screens.test.mjs are updated, with new assertions for each fix.
• scripts/check-dead-code.mjs: clean.
• Driven by hand at 375×812 and 1400×900 with the dev clock on a Wednesday at 11:00: corner positions, labels, focus, history length after Check again, and the menu returning to the list.

For review

• On a phone, the plate's side inset makes names like "University Hall 043" wrap onto two lines.
• Hovering ← or ☰ now dims the glyph instead of showing a filled disc.

🤖 Generated with Claude Code