feat(browser): browser hardening bundle — find-in-page, downloads, zoom, security indicator

Rebasing feat/browser-hardening-bundle onto updated main revealed that
from_state was dropped from BrowserView (the bundle simplified new but
forgot from_state). browser_pane.rs::new_from_state calls it for tab
state restore on pane reopen.

Adds from_state mirroring new: uses BrowserModel::restore, builds
webviews from all persisted tabs, wires url_editor + find_editor
subscriptions and event_rx the same way.

84 browser tests pass (downloads, zoom, popup_policy, url_input,
persistence).

Author: BunsDev