- Add WindowsConsole.IsConsoleAvailable() to detect real console handles
- Update PlatformConsoleFactory to fall back to FallbackConsole when
  Windows console isn't available (piped/redirected scenarios)
- Remove ENABLE_VIRTUAL_TERMINAL_INPUT flag which interferes with
  ReadConsoleInputW structured events
- Simplify output mode configuration

WIP: Interactive mode still not working in Windows Terminal - needs
better diagnostics (issue #72) to debug further.

The ReadInputAsync method was marked async but had no await statements,
causing it to run synchronously and block the UI thread. This resulted
in nothing rendering when using WindowsConsole on Windows Terminal and
ConEmu.

Added Task.Yield() to properly yield control back to the event loop,
allowing rendering to proceed while waiting for input.

Also added comprehensive diagnostic tracing to the platform console
layer for easier debugging of console initialization and input handling.

Replace Task.Yield with Task.Delay(1) for better async scheduling. Filter phantom WINDOW_BUFFER_SIZE_EVENTs that don't actually change size.

Cache console dimensions to avoid repeated P/Invoke calls on Windows.

Previously, DiffingTerminal accessed Width/Height properties on every
character write during rendering (~4,800 times per frame on 80x30 terminal).
On Windows, Console.WindowWidth/Height make uncached P/Invoke calls to
GetConsoleScreenBufferInfo, causing 22-60ms render times.

Now cache dimensions and only refresh during HandleResize(), reducing
P/Invoke calls from ~4,800/frame to 2/frame. Render times improved from
22-60ms to 0.02-0.08ms (~1000x faster).

Linux was unaffected as ConsolePal.Unix.cs already caches these values
using signal-based invalidation (SIGWINCH).

Replace complex P/Invoke-based input loop with simpler Console.ReadKey
approach. The new implementation:

- Uses Console.KeyAvailable to check for input without blocking
- Reads keys via Console.ReadKey when available
- Polls for window resize events during idle periods
- Uses Task.Delay(1ms) for responsive cancellation

This eliminates the need for WaitForSingleObject, ReadConsoleInputW,
and manual INPUT_RECORD handling while maintaining the same functionality.