feat(sdk): add force install option

[samzong]

What's changed?

• Add an explicit force install option across the TypeScript, Go, and Rust SDKs.
• Wire --force through the Go Cobra adapter.
• Keep default conflict handling safe while preventing partial writes when conflicts exist.
• Add shared golden coverage for force overwrites, mixed conflict blocking, and dry-run mixed-plan rendering.

Why

• Users need an explicit way to replace unmanaged or different-owner skill installs after reviewing conflicts.

Verification

• node scripts/check.mjs
• pre-ship --committed