Refactor GhosttyLibVt to support both shared and static library builds via a shared initLib helper that accepts a LinkMode. The shared and static entry points (initShared, initStatic) delegate to this common path. For static builds, compiler_rt and ubsan_rt are bundled to avoid undefined symbol errors. Debug symbols (dsymutil) are skipped for static libs since they are not linked. The install artifact uses a "-static" suffix internally but installs as "libghostty-vt.a" via a new installLib method. Wasm is excluded from static builds since it has no meaningful static vs shared distinction.