feat: v0.4.0 Focus + Drag + Resize

Adds focus/raise/lower/get_focused API with click-to-focus auto-routing
(hud-tier never focusable), drag-by-title-bar with 32px screen-clamp,
resize via SE-corner handle with min/max_size clamps. Drag and resize
move bounds outside the layout-fn via a per-window bounds_override
that shadows resolve_bounds across render + dispatch + point_in_any_panel.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

manifest.lib

@@ -1 +1 @@
-{"id":"lib-core.panel","version":"0.3.0","api_min":"0.1","deps":[]}
+{"id":"lib-core.panel","version":"0.4.0","api_min":"0.1","deps":[]}