fix(windows): resolve absolute opencode binary for schtasks tasks

[CENFARG]

Closes #25

Summary

• Windows schtasks tasks now invoke the absolute opencode binary instead of a bare opencode name that Task Scheduler cannot resolve (LastResult 2147942402 / 0x80070002).
• Tasks redirect output to the scoped log via a cmd wrapper, matching the launchd/systemd backends.
• Not done: schtasks /Create has no WorkingDirectory flag; tracked as follow-up via XML import. This PR fixes resolution + log redirect only.

Changes

File	Change
src/index.ts	Add findOpencodeWindows() (scoop shim dir, default install locations, where.exe); wire into findOpencode() on win32; cmd-wrapper log redirect for schtasks tasks (55 lines)
README.md	Document Windows binary resolution (1 line)

Test plan

• Typecheck passes
• Build passes
• Canary schtasks job verified: LastResult 0 with absolute path (was 2147942402 with bare binary)
• schtasks-only change; launchd/systemd/cron paths untouched
• Local branch only; main untouched (2 commits on top of cd0b623)

Before/after /TR:

Before: /TR bare "opencode run ..." -> LastResult 2147942402 (0x80070002). After: /TR con ruta absoluta via cmd wrapper -> LastResult 0.

Known limitation

Paths with spaces + npm shim .cmd untested; the canary used the scoop .exe shim.

Example generated /TR command (captured output)

cmd.exe /c "C:\Users\canary\scoop\shims\opencode.exe run -- "hello canary" >> C:\Users\canary\.cache\opencode\logs\scheduler\scope-abc123\nightly.log 2>&1"