fix: UTF-8 console output on Windows (Issue #201)

[vmvarela]

Summary

Implements SetConsoleOutputCP(65001) and ENABLE_VIRTUAL_TERMINAL_PROCESSING on Windows startup so --table box-drawing characters render correctly in default cmd.exe.

Changes

• src/main.zig: Added Windows API extern declarations for SetConsoleOutputCP, GetStdHandle, GetConsoleMode, SetConsoleMode
• src/main.zig: Added setupConsoleOutput() function (compile-time gated on Windows)
• src/main.zig: Call setupConsoleOutput() at startup in main() before any I/O

Implementation Details

• Uses extern "kernel32" with callconv(.winapi) — no new dependencies
• Compile-time conditional via @import("builtin").os.tag == .windows — zero overhead on non-Windows
• Best-effort: ignores return values per issue scope (no-op on failure)
• Fixed STD_OUTPUT_HANDLE = -11 bug (u32 can't hold -11) → @bitCast(@as(i32, -11))
• Fix: Inlined std.os.windows types directly (removed intermediate windows import)
• Fix: Added comment // 0xFFFFFFF5 for readability
• Fix: Added INVALID_HANDLE_VALUE check — guards against redirected stdout where GetStdHandle returns invalid handle

Testing

• ✅ zig build (native) succeeds
• ✅ zig build -Dtarget=x86_64-windows-gnu -Dbundle-sqlite=true succeeds
• ✅ zig build -Dtarget=x86-windows-gnu -Dbundle-sqlite=true succeeds
• ❌ zig build -Dtarget=aarch64-windows-gnu -Dbundle-sqlite=true fails — pre-existing carquet/arocc issue unrelated to this change

Oracle Reviews

All 3 phases reviewed and approved:

1. Phase 1: Extern declarations — fixed STD_OUTPUT_HANDLE bug
2. Phase 2: setupConsoleOutput() function — correct implementation
3. Phase 3: Call in main() — correct placement

Closes #201