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/.gitignore

@@ -0,0 +1,4 @@
+*.exe
+glm_tiny/
+olmoe_hf/
+olmoe_i4/