Resolve CSS selectors to source file paths

[BraedenBDev]

An AI coding agent reviewing PointDev output requested source file mapping as the single highest-value addition for one-shot fixes:

"Resolve CSS selectors to source files. .hero-content to src/components/Hero.tsx:275. This skips my entire exploration step."

Currently PointDev captures the CSS selector and React component name (when available), but not the source file and line number. React fiber internals include _debugSource in development builds, which contains the file path and line number. This should be extracted when available.

For production builds without debug info, source map resolution could map compiled class names back to source locations. This is a stretch goal. The dev-build path covers the primary use case (developers testing their own sites).

Related to M7 (framework detection) in the milestone plan.