event_loop, widget, input: pointer-dwell tooltips, global drag coords, foreign-toplevel name cascade

`Button::tooltip( text )` registers a hint string that fires after a 600 ms pointer dwell. `LaidOutWidget` gains a `tooltip: Option<String>` field, `Element::tooltip()` exposes it to the input layer, and the existing pointer-hover path now calls `arm_tooltip` on hover-enter and `cancel_tooltip` on hover-leave / touch. The deadline is polled alongside `next_long_press_wakeup` in `try_run` so an idle pointer still gets a wake-up at the firing instant; on fire, `tooltip_overlay()` synthesises an `OverlaySpec` — a rounded `text_primary @ 95%` pill drawn with `bg` text — anchored above the hovered widget, flipping below or clamping inside the screen if it would clip, and pushed alongside the app's own overlays both in the redraw path and in `reconcile_overlays` so the layer surface is created the same frame the tooltip becomes visible. Pointer-only by design: touch events explicitly cancel because a tap-and-release should never linger into a hint. The `showcase` example wires `.tooltip(..)` on the three button variants as a smoke test.
The drag pipeline now reports positions in main-surface (global) coordinates instead of per-surface. `surface_offset_for( focus )` derives the top-left of an overlay surface from `SurfaceState::layer_anchor` — newly stored at `reconcile_overlays` time from `OverlaySpec::anchor` — combined with the main surface's dimensions; `on_drag_move`, `on_drop`, the synthetic move emitted on drag-promotion in `pointer.rs`, and the `pending_drag_inits` push site in `gesture::start_drag` all translate before handing coordinates to the app. The motion and release paths additionally `request_redraw()` every overlay so a dock-style drop target painted on an `Anchor::Bottom` layer surface gets repainted as the drag moves — without that, the visible drop indicator only updates when the cursor re-enters the main surface. Drops still target whichever surface fired the release; only the coordinates are unified.
`ForeignToplevelListHandler` previously read `app_id` directly via `ForeignToplevelList::info()`. Clients that never set `app_id` (some winit-windowed compositors, simple test clients) were silently invisible to crustace-style docks because the empty string fell through `unwrap_or_default()` and the dock then keyed entries off `""`. `toplevel_display_id()` cascades: prefer `app_id` for desktop-entry matching, fall back to `title` for human-readable identification, and finally to the protocol-issued `identifier` which is always present and unique per handle. Applied to both `new_toplevel` and `update_toplevel`.
`theme::system_fontdb()` lazily loads the system font database once via `OnceLock` and reuses the `Arc` for every `decode_svg_bytes` call. resvg's default `Options::fontdb` is empty, so any SVG containing `<text>` rendered with the built-in fallback font or no font at all; with the system DB attached, icons and decorative SVGs with embedded labels now resolve glyphs correctly. Cached because `load_system_fonts()` walks every font path on the system and is comfortably tens of milliseconds on a cold cache — not something to repeat per icon decode.
`themes/default/theme.json` tweaks one variant's slot palette: `surface-alt` from `@indigo/D9` to `@white/D9` and `text-primary` from `@white` to `@navy`, plus a cosmetic re-alignment of the `"value"` columns in the same slots block.

src/widget/mod.rs

@@ -423,6 +423,7 @@ pub struct LaidOutWidget<Msg: Clone>
 	/// dispatch can pick the right shape without re-walking the
 	/// element tree.
 	pub cursor:             crate::types::CursorShape,
+	pub tooltip:            Option<String>,
 }
 
 impl<Msg: Clone> Clone for LaidOutWidget<Msg>
@@ -438,6 +439,7 @@ impl<Msg: Clone> Clone for LaidOutWidget<Msg>
 			handlers:           self.handlers.clone(),
 			keyboard_focusable: self.keyboard_focusable,
 			cursor:             self.cursor,
+			tooltip:            self.tooltip.clone(),
 		}
 	}
 }
@@ -664,6 +666,16 @@ impl<Msg: Clone> Element<Msg>
 		}
 	}
 
+	/// Add an arm here to opt a widget kind into the auto-tooltip flow.
+	pub fn tooltip( &self ) -> Option<&str>
+	{
+		match self
+		{
+			Element::Button( b ) => b.tooltip.as_deref(),
+			_                    => None,
+		}
+	}
+
 	/// Snapshot the widget's callbacks/value into a [`WidgetHandlers`] for
 	/// O(1) dispatch later. Called once per focusable leaf during the layout
 	/// pass; the handlers are then stored alongside the rect in