fix(windows): suppress console popup on child_process calls (#498)

On Windows, v0.9.5's detached shared daemon (#411) has no inherited console,
so any console-subsystem child it spawns gets a fresh visible console window
unless the spawn passes `windowsHide: true`. The fix adds the flag to all
ten `spawnSync` / `execFileSync` / `execSync` call sites across extraction,
sync, installer, and the WASM-flags relaunch. macOS/Linux ignore the option,
so this is a no-op elsewhere.

Fixes #485, #510, #530.

Co-authored work:
- #498 (csw-chen) — full sweep across extraction, sync, installer, and wasm-runtime. **This is the change being merged.**
- #505 (yushengruohui) — independently identified and fixed the 7 git execFileSync sites. Superseded by #498's broader sweep; same diagnosis.
- #521 (JirA44) — independently identified and fixed the WASM-runtime spawnSync re-exec. Superseded by #498's broader sweep; same diagnosis.

Validated on Windows 11 ARM64 (Parallels): a detached parent's 15 git spawns produce 15 visible black flash-windows without the fix and 0 with it.

src/sync/worktree.ts

@@ -35,6 +35,7 @@ export function gitWorktreeRoot(dir: string): string | null {
       cwd: dir,
       encoding: 'utf8',
       stdio: ['ignore', 'pipe', 'ignore'],
+      windowsHide: true,
     }).trim();
     return out ? realpath(out) : null;
   } catch {