## Why

BlackMagic replaced FASM for shellcode generation but lost two useful capabilities:

1. **Non-blocking remote execution** (`InjectAndExecuteEx`): FASM's managed wrapper returned a thread handle without waiting. BlackMagic only has blocking `Execute()`. For DLL injection, a non-blocking variant avoids hanging when the target is slow to load.

2. **Text-based assembly**: FASM allowed building shellcode from assembly text (`AddLine("pushad")`). BlackMagic requires hand-assembled `byte[]`. For prototyping, debugging, and one-off shellcode, text assembly is faster to write and easier to review. A managed assembler eliminates the native FASM DLL dependency while keeping the ergonomic benefit.

## What Changes

- Add `InjectAndExecuteEx()` to `BlackMagic` and `BMThread`: inject code then create a remote thread without waiting, returning the thread handle.
- Add `AsmBuilder` class: pure C# x86 text assembler that converts instruction text to `byte[]` machine code. Supports common shellcode instructions (mov, push, pop, call, jmp, ret, nop, pushad/popad, test, je, jne, inc, add, sub, xor, etc.).
- Add `InjectAndExecute(string asm)` and `InjectAndExecuteEx(string asm)` overloads that accept assembly text, assemble via `AsmBuilder`, then inject+execute.
- Add `SetPassLimit()` to `AsmBuilder` for label resolution iteration control.

## Capabilities

### New Capabilities
- `non-blocking-execute`: Non-blocking remote thread creation that returns a handle without waiting for exit.
- `text-assembler`: Pure C# x86 text assembler converting assembly source to byte arrays without native dependencies.

### Modified Capabilities
<!-- None — additive features only. -->