observers.js leaks delegated click/keydown handlers on the shared #app container #405

Found during the review of #402 (merged), and pre-existing on master: public/observers.js (~182) binds its delegated click and keydown handlers to the shared #app container and never removes them.

After visiting the Observers page, those handlers keep running on every later page. This is the same leak class #402 fixed in compare.js, where it broke the observers slide-over (Kpa-clawbot#1056 AC#4).

Required work

• Bind the handlers to the observers page's own container, or remove them in the page's destroy().
• Grep public/*.js for other app.addEventListener( / document.addEventListener( calls in page modules without a matching removal in destroy(), and fix them the same way.
• Add a regression test: navigate observers → another page, then assert that no observers handler fires.