Fix release-mode crashes: inline asm register clobbers and fastcall ABI

Root cause: hook.fastcall used "r" constraints + explicit MOV to set
ECX/EDX. LLVM can allocate "r" inputs to clobbered registers, causing
cross-assignment (ecx_in→EDX, edx_in→ECX) or function address stomping
when func lands in ECX/EDX. Debug works by luck (trivial regalloc);
Release optimizes aggressively and hits the conflicts.

Fix: explicit "{ecx}", "{edx}", "{eax}" register constraints in zhook
fastcall — compiler places values directly, no MOV needed, no ambiguity.

Also fix 9 inline asm blocks across main.zig, interact.zig,
screenshot.zig, markers.zig missing ECX/EDX clobbers after CALL
instructions. Without clobbers the optimizer assumes registers retain
input values after the call — stale reuse in release builds.

Other changes in this commit:
- Rename markers→worldmarkers (build flag, DLL, Lua table)
- Rename assetfix→looseassets
- lua.zig: add .never_tail to pushcclosure, pcall, openlib, pushnumber
- Move internal marker functions into WorldMarkers Lua table via openlib
- Remove unused GetCurrentAreaId function
- Fix cleanup_file_handle_hook.original() → .callOriginal()

src/screenshot/screenshot.zig

@@ -288,7 +288,7 @@ fn luaPushNumber(L_ptr: usize, n: f64) void {
           [lo] "r" (raw[0]),
           [hi] "r" (raw[1]),
           [func] "r" (@as(u32, 0x6F3810)),
-        : .{ .eax = true, .edx = true, .memory = true, .cc = true }
+        : .{ .eax = true, .ecx = true, .edx = true, .memory = true, .cc = true }
     );
 }