Remove ambient validation markers, show ptr64 as void*, add struct types to picker, add README

- Remove M_ERR and M_PTR0 ambient markers from compose (validation only during inline edit)
- Change ptr64 display name to void* in kKindMeta
- Type picker now includes custom struct type names from the tree
- Controller handles struct type selection from picker
- Add project README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -0,0 +1,22 @@
+# ReclassX
+
+A hex editor for reading live process memory. It shows structs, pointers, arrays, and padding so you can see how data is laid out and how it connects.
+
+Work in progress.
+
+![screenshot](build/screenshot.png)
+
+## Build
+
+Requires Qt 6, QScintilla, and MinGW on Windows.
+
+```
+cmake -B build -G Ninja
+cmake --build build
+```
+
+QScintilla must be built first as a static lib. There is a helper script:
+
+```
+powershell -File scripts/build_qscintilla.ps1
+```