docs: update build CLI defaults

[grzdev]

Summary

• update the vite build CLI guide to document the current --target and --minify defaults
• update vite build --help to include oxc as a valid minifier and show oxc as the default

Problem

Vite 8 uses baseline-widely-available as the default build.target, and build.minify supports oxc, terser, and esbuild, with oxc as the default for client builds.

The build options docs and implementation already reflect this, but the CLI guide and --minify help text still referenced older defaults.

Fix

• update the --target row in the CLI guide to show baseline-widely-available
• update the --minify row in the CLI guide to show oxc as the default and include it in the supported values
• update the --minify help text in packages/vite/src/node/cli.ts to match current behavior

Verification

pnpm exec tsx packages/vite/src/node/cli.ts build --help
pnpm exec oxfmt --check packages/vite/src/node/cli.ts docs/guide/cli.md
git diff --check -- packages/vite/src/node/cli.ts docs/guide/cli.md