Complete observer quick-inspection keyboard and return navigation

[n30nex]

Observer quick inspection is reachable from packet and route investigation. Its Close button works by mouse or keyboard and restores trigger focus, but Escape currently does not dismiss it: the generic ModalOverlay delegates Escape to callers and App's quick-observer instance has no handler. Reproduced in the development composition during route #85 browser checks.

Track the next connected-navigation slice here: add top-layer Escape handling without closing underlying panels, preserve originating route/packet/dashboard state through observer dashboard navigation, and cover observer-to-packet overlay stacking. Existing route report -> analyzer -> map -> Close and observer quick-panel Close paths are validated. Do not count broader cross-tab return navigation as complete yet.

[n30nex]

Starting this slice on #85 (3b3abdcc). No upstream refresh is needed. I reproduced the missing observer Escape handler and traced observer-to-packet stacking to separate overlay flags; dashboard navigation also unmounts the original tab.

The focused change will reuse existing detail components with ordered panel navigation, top-layer Escape/Close and keyboard advert actions. Opening a canonical observer dashboard will retain one originating screen under its original URL context so Back/return restores filters, scroll, selection and panels. Explicit tab/region exits release it; shared/reloaded dashboards stay standalone. Native Pi, desktop/phone, EN/FR and source/changelog validation will follow before review handoff.