iOS 26 Liquid Glass selection pill no longer cropped at top

The v1.4.0 Issue #2 fix clipped the platform-view container to stop
the Liquid Glass drop shadow from bleeding over modal bottom sheets.
The same clip was also cutting off the iOS 26 tab bar's selection
pill during its morph animation between tabs.

Fix: container still clips (shadow containment preserved), but the
UITabBar is positioned 14pt below container.topAnchor in all 5
layout sites, and getIntrinsicSize reports barHeight + 14pt. The
selection pill — including rapid morph between tabs — now renders
fully inside the clipped container. Bar's visible position on screen
is unchanged.

Example app:
- New "#33: SVG in CNTabBar" reproduction screen
- New "Stack+Positioned tab bar" reference screen
- "CNTabBar split-search clip" enhanced with modal test + teal bg
- iOS deployment target bumped 14.0 -> 15.0

Known issue documented in CHANGELOG and inline Swift comment:
simulator Liquid Glass rendering differs from real device; verify on
hardware before treating visual artifacts as bugs.

Pana: 160/160.

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