Show keybinding in tooltips for controls that have one

[MasonRhodesDev]

ActionTooltip (desktop/src/app.rs:617) and its helper action_tooltip_view(label, cx) (desktop/src/app.rs:2393) are used at many sites (app.rs, custom_actions_modal.rs, left_sidebar.rs, ...) but only render a label. Extend them so controls backed by a configurable ShortcutAction (core/src/shortcuts.rs) also show the current binding — e.g. "New Task ⌘T" or "Previous Tab Ctrl+Shift+[".

Proposed shape: a trait on GUI elements that expresses "this element is the handle for feature X", rather than a parallel helper. Anything that implements the trait picks up the tooltip's shortcut chip automatically and stays in sync with the user-configurable binding.

Sketch:

trait WithShortcut {
    fn with_shortcut(self, action: ShortcutAction) -> Self;
}

…implemented for the element types we pass to .tooltip(...). Internally it attaches the ShortcutAction to the element so the tooltip renderer can resolve the live binding via project_store.ui.shortcuts.binding_for(action) and pretty-print via keybinding_token_label (desktop/src/shortcuts.rs:143). The shortcut chip renders dim/monospace to the right of the label.

Callers update from:
.tooltip(|_w, cx| Self::action_tooltip_view("New Task", cx))
to:
.tooltip(|_w, cx| Self::action_tooltip_view("New Task", cx))
.with_shortcut(ShortcutAction::NewTask)

Update the existing .tooltip(...) sites whose controls correspond to a ShortcutAction (NewTask, NewTabInCurrentTask, CloseCurrentTab, Next/PreviousTab, Next/PreviousTask, CycleProjects, and once #62 lands — ZoomIn/Out/Reset). Label-only tooltips for controls with no shortcut stay as-is.

Naming and trait surface TBD — the point is that the shortcut annotation lives on the element, not in a parallel helper.