libghostty-vt WASM demos

ghostty-vt.wasm is built from ghostty-org/ghostty (MIT) with zig build -Demit-lib-vt -Dtarget=wasm32-freestanding. The pages are Ghostty's own examples.

• wasm-vt: feed VT data to a terminal, read back its text
• wasm-sgr: parse SGR styling sequences
• wasm-key-encode: encode key events as escape sequences