Thread Safety: Synchronize MockNcursesBridge.setTerminalSize()

[sfloess]

Part of #224: Improve Thread Safety in Component and Container

Scope

Address issue #5 from the parent issue:

MockNcursesBridge.setTerminalSize() not synchronized (MockNcursesBridge.java lines 129-159)

• Does not synchronize access to width/height/screen fields
• Concurrent calls to getTerminalWidth()/getTerminalHeight() could read torn/inconsistent values
• Concurrent resize could cause ArrayIndexOutOfBoundsException if screen buffer is swapped mid-operation

Proposed Fix

Add synchronized modifier to setTerminalSize() and coordinate with getTerminalWidth(), getTerminalHeight(), and screen buffer access methods.

Acceptance Criteria

• setTerminalSize() is synchronized
• Width/height/screen reads are consistent with writes
• No torn reads during concurrent resize
• Existing tests pass