Extract reusable bubble menu components

ui/components/bubble_menu/README.md

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+# Bubble menu authoring
+
+Instance `bubble_button.tscn` for each action, or attach `bubble_button.gd`
+to an existing Button. Set its neutral size, desktop and compact anchors,
+font-size limits, and deterministic motion values in the Inspector. A label
+child can be assigned through `label_control_path` when wrapped text is needed.
+Text size is calculated once per layout from the neutral smaller dimension and
+the profile ratio.
+
+Place the buttons under a Control using `bubble_cluster.gd`. Give the cluster
+the ordered BubbleButton references with `configure()`, then call
+`apply_layout()` when its available size or responsive layout changes. The
+button order defines explicit keyboard and controller focus neighbors. Compact
+anchors and minimum sizes remain authored per button.
+
+The shared profile owns the palette, rounded styles, proportional-font ratio,
+hover response, and contact tuning. Labels, actions, sizes, anchors, per-button
+motion, responsive wrapping, availability, and confirmation behavior remain
+owned by the menu. Connect each Button's `pressed` signal in that parent menu.
+
+`motion_scale` defaults to `1.0`. Setting it to `0.0` removes idle drift and
+deformation while retaining hover and focus feedback.
+
+Contact is a deterministic, bounded visual correction around authored anchors.
+Real physics is intentionally avoided so layouts, focus order, and hit targets
+remain stable.