Add keyboard shortcuts for common browser actions

[niklabh]

Description

Oxide currently lacks keyboard shortcuts for common actions. Power users expect to be able to navigate with the keyboard. This is listed in the roadmap under Phase 9 (Platform Maturity).

Suggested shortcuts

Shortcut	Action
Ctrl/Cmd + L	Focus the URL bar
Ctrl/Cmd + T	New tab
Ctrl/Cmd + W	Close current tab
Ctrl/Cmd + R	Reload current page
Alt + Left	Navigate back
Alt + Right	Navigate forward
Ctrl/Cmd + D	Add/remove bookmark
Ctrl/Cmd + Shift + J	Toggle console panel

Implementation hints

egui provides keyboard input via ctx.input():

if ctx.input(|i| i.modifiers.command && i.key_pressed(egui::Key::L)) {
    // Focus URL bar
}

Files involved

• oxide-browser/src/ui.rs — add shortcut handling in the main update() loop

Difficulty

Beginner — each shortcut is a few lines of code. Can be done incrementally (start with 2-3 shortcuts in one PR).