Extract cssAttrSelector to packages/core/src/utils/cssSelector.ts and
use it (or CSS.escape for browser-side code) at all 12 sites that
previously interpolated raw user-authored values into querySelector
attribute selectors. A " in a composition ID, script src, or
data-start value would produce a malformed selector that throws.
Node-side (core compiler/parser): uses the shared cssAttrSelector.
Browser-side (runtime, studio): uses native CSS.escape().
Supersedes #1568 which fixed only the 3 bundler sites.
