Define the win32 engine; add a dump source and physical sigscan

Name and isolate the Windows engine as one of potentially several. The
public surface moves to include/win32.h with an opaque vmie_win32 handle
(vmie_win32_open/close/mem); the engine's Windows internals — host bring-up,
the struct-offset profile, process/module/PE/text decode — live under
src/engine/win32. The generic address-space layer stays in src/engine
(gva.c + engine-arch.h, carrying no offset table): gva.c is de-profiled, and
CR3 bring-up reaches the hot translator through a cold gva_translate bridge
so the zero-copy hot path stays private and inlinable.

A memory source is now first-class and public: vmie_mem_open/_open_segs/
_close open a flat dump (or an explicit segment map) as a vmie_mem, with
gpa_seg promoted to the public contract. The physical signature scan is
exposed source-agnostically: sig_scan_mem returns GPAs for any vmie_mem,
sig_scan_sources scans several sources with per-source attribution, and
sig_from_bytes builds an exact needle from a byte span. The pure matcher is
unchanged; dumps and the live engine image are scanned uniformly, neither
needing the other.

CMakeLists.txt

@@ -11,17 +11,19 @@ option(VMIE_LTO "Enable LTO" OFF)      # build-only; shipped default is -O2, no
 add_library(vmie STATIC
         src/core/gpa.c
         src/engine/gva.c
-        src/engine/host.c
-        src/engine/pe.c
-        src/engine/proc.c
-        src/engine/profile.c
-        src/engine/text.c
+        src/engine/sigphys.c
+        src/engine/win32/host.c
+        src/engine/win32/pe.c
+        src/engine/win32/proc.c
+        src/engine/win32/profile.c
+        src/engine/win32/text.c
         src/handlers/scan.c
         src/handlers/sigscan.c)
 target_include_directories(vmie
         PUBLIC  ${CMAKE_CURRENT_SOURCE_DIR}/include              # public API: include/*.h
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src/core/include     # private: core.h
-                ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/include)  # private: engine.h, contract.h
+                ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/include   # private: engine-arch.h, pe.h
+                ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/win32)    # private: engine-win32.h, contract.h
 target_compile_options(vmie PRIVATE -O2 -Wall -Wextra)
 if(VMIE_LTO)
     target_compile_options(vmie PRIVATE -flto)
@@ -39,10 +41,10 @@ set(VMIE_STARTUP ${CMAKE_CURRENT_BINARY_DIR}/vmie-startup.exe)
 add_custom_command(
         OUTPUT  ${VMIE_STARTUP}
         COMMAND ${MINGW_CC} -O2 -Wall -Wextra -static -s
-                -I${CMAKE_CURRENT_SOURCE_DIR}/src/engine/include
-                -o ${VMIE_STARTUP} ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/guest.c
-        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/guest.c
-                ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/include/contract.h
+                -I${CMAKE_CURRENT_SOURCE_DIR}/src/engine/win32
+                -o ${VMIE_STARTUP} ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/win32/guest.c
+        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/win32/guest.c
+                ${CMAKE_CURRENT_SOURCE_DIR}/src/engine/win32/contract.h
         COMMENT "Cross-compiling vmie-startup.exe (mingw-w64, x86-64)"
         VERBATIM)
 add_custom_target(vmie-startup ALL DEPENDS ${VMIE_STARTUP})