Page modules leak delegated handlers on #app/document (compare, channels, live) — remainder of #405 #428

Remaining part of #405 (the observers.js part was fixed in #419, merged as 20513d48). The sweep in #419 found 15 more page-module handlers that are bound to the shared #app/document container and never removed in the page's destroy():

• public/compare.js: 1
• public/channels.js: 6
• public/live.js: 8

The full list with line numbers is in the #419 PR description, under "Same-class leaks found but NOT fixed".

The review of #419 confirmed that two of them are live on master [T]. After 3 visits followed by Nodes, #app carries keydown ×3 from Compare and click ×3 from Channels.

Required work

• Fix each site the same way as fix(ui): stop observers.js leaking delegated handlers on #app (#405) #419: bind to the page's own container, or remove the handler in destroy().
• Each page gets a red/green regression test: N visits, then another page, then assert that no handlers are stacked or still firing.
• Keep page behaviour unchanged. That includes Live's map/WebSocket handling: note the known Live init/teardown races and do not regress them.