AVD creation should enable GPU acceleration in config.ini

## Problem

When creating an AVD via `AvdManagerRunner.GetOrCreateAvdAsync()`, the resulting `config.ini` has `hw.gpu.enabled = no` by default. This causes the emulator to show a black screen and fail to boot on newer API levels (36+), because SurfaceFlinger requires GPU support.

## Expected Behavior

After AVD creation, patch `config.ini` to set:
- `hw.gpu.enabled = yes`
- `hw.gpu.mode = auto` (already default)

This matches what `dotnet/android`'s `CreateAndroidEmulator.cs` MSBuild task does — it patches RAM size and disk partition after creation.

## Proposed Solution

Add a post-creation config patching step in `GetOrCreateAvdAsync()` that:
1. Locates the created AVD's `config.ini` (from the returned `AvdInfo.Path`)
2. Sets `hw.gpu.enabled = yes`
3. Optionally allows callers to provide additional config overrides (e.g., RAM size, disk partition size)

## Context

Discovered while debugging emulator boot failures with API 36 system images. The emulator starts but SurfaceFlingerAIDL service can't initialize without GPU → `sys.boot_completed` never becomes `1` → `pm install` fails with `Can't find service: package`.