`submit_command` matched every browser's "Enter to navigate" intent
to `open_tab(url)`, which always inserts a new `BrowserTab`. So
typing `google.com` and hitting Enter on a new-tab page would leave
both the new-tab and a fresh google.com tab in the sidebar.
Mirror the same in-place navigation rule the shell-level code now
uses: `navigate_active_tab(url)` for the Navigate and Search
intents, with `open_tab` as the fallback when there's no active tab
yet. Tab count only goes up when the user explicitly hits + New Tab.
cargo test --workspace: 440 passed, 0 failed.
ZacharyZhang-NY
c95e3665c6