ci: add native Windows compatibility harness

[KenTaniguchi-R]

Summary

• add a manually dispatchable native windows-2025 matrix for Node 20, 22, and 24
• run build, typecheck, all shared and relay tests, and 51 explicitly platform-neutral CLI tests on Node 24
• prove the packed CLI .cmd shim runs from clean paths containing spaces while ordinary npm installation remains blocked until Support Windows as a native AgentCall callee #251
• pin current setup, doctor, and listener failures to the documented managed-policy boundary
• document all functional blockers and the Daytona/manual end-to-end probe

Local verification

• pnpm -r build
• pnpm -r typecheck
• pnpm -r test: shared 166, CLI 932 with 5 live probes skipped, relay 256
• pnpm docs:check: 4 contract/site tests and 25 pages validated
• CLI test:windows: 51 passed
• workflow YAML parses and all actions are SHA-pinned

Native verification

• GitHub Actions run 30863691728 passed on Microsoft Windows Server 2025
• Node 24: monorepo build/typecheck, shared 166, relay 256, and portable CLI 51 tests
• Node 20/22/24: packed install harness, generated agentcall.cmd --version/--help, and exact Support Windows as a native AgentCall callee #251 blocker assertions
• macOS/Linux packed consumers remain green across Node 20/22/24

Closes #250