Windows 11 native port, phase 1: MinGW-w64 static build, compat shims, setup + docs (#40)

* fix: Windows port audit fixes — _FILE_OFFSET_BITS guard, O_BINARY st.h, getrusage peak, oracle diagnostic, setup.sh wmic

Audit remediation (all MEDIUM issues fixed):
- compat.h: compile-time #error if _FILE_OFFSET_BITS < 64 on _WIN32
- compat.h: COMPAT_O_RDONLY macro (O_RDONLY|O_BINARY on Windows, belt-and-braces)
- st.h: use COMPAT_O_RDONLY in both open() call sites (plan §1 row 1)
- compat.h: getrusage shim now uses PeakWorkingSetSize (ru_maxrss = peak, not current)
- glm.c: oracle mismatch diagnostic — prints position/expected/got on TF failures
- setup.sh: replace deprecated wmic with /proc/meminfo (MSYS2 provides it)
- .gitignore: *.exe, glm_tiny/, olmoe_hf/, olmoe_i4/

LOW issues addressed:
- _FILE_OFFSET_BITS guard prevents silent 32-bit off_t wrap at >4GB offsets
- coli Windows venv path (Scripts/python.exe) fixed earlier
- posix_fadvise do{}while(0) kept intentionally — no caller checks return code

Verification: oracle 32/32, 27/27 Python tests, rename EEXIST, >4GB pread offset.

* docs: add Windows 11 native port section to README

- Toolchain: MinGW-w64 (winlibs or MSYS2), GCC 16.1 tested
- Build instructions: make glm.exe, tiny oracle verification
- Runtime: SNAP=..., coli chat, coli serve all work
- Status: Phase 1 complete (compiles, correct, static-linked)
- Update platform requirements to include Windows 11 natively

c/st.h

@@ -76,11 +76,11 @@ static inline float f16_to_f32(uint16_t h) {
 
 static int st_open_fd(shards *S, const char *path) {
     for (int i = 0; i < S->nfd; i++) if (!strcmp(S->paths[i], path)) return S->fds[i];
-    int fd = open(path, O_RDONLY);
+    int fd = open(path, COMPAT_O_RDONLY);
     if (fd < 0) { perror(path); exit(1); }
     S->paths[S->nfd] = strdup(path); S->fds[S->nfd] = fd;
 #ifdef O_DIRECT
-    S->dfds[S->nfd] = open(path, O_RDONLY | O_DIRECT);   /* eager: lookup poi thread-safe */
+    S->dfds[S->nfd] = open(path, COMPAT_O_RDONLY | O_DIRECT);   /* eager: lookup poi thread-safe */
 #elif defined(__APPLE__)
     S->dfds[S->nfd] = compat_open_direct(path);          /* macOS: F_NOCACHE ~ O_DIRECT */
 #else