fix(ui): contain custom panel inside ha-drawer .app-content frame without bleeding under sidebar

[spelech]

Summary

• Replaces position: absolute; top: 0; left: 0; width: 100% in custom_components/google_assistant_entity_console/static/panel.js with normal-flow position: relative; width: 100%; max-width: 100%; height: calc(100vh - var(--safe-area-inset-top, 0px) - var(--safe-area-inset-bottom, 0px)); contain: layout paint; isolation: isolate; z-index: 1.
• In Home Assistant 2026.x, <ha-drawer>'s .app-content uses position: static with padding-inline-start: var(--ha-sidebar-width) (256px expanded, 56px collapsed). Using position: absolute; left: 0 caused <google-assistant-entity-console-panel> to position relative to the viewport at x = 0, bleeding underneath <ha-sidebar>.
• Adds Playwright E2E regression test test_ha_drawer_sidebar_frame_containment verifying x == 256 and width == 1184 inside a 1440x900 <ha-drawer> layout.
• Bumps manifest.json version to 3.0.1 to bust browser cache on panel registration.

Visual Verification