Adds frontend/src/styles.css extracted from the confirmed prototype
(paper/ink/pine palette, Fraunces/Inter/IBM Plex Mono type system,
catalog-tag motif) and makes the minimal JSX adjustments needed for
each component to pick up the styling: wordmark heading, search icon,
upload button icon + modal header/footer, folder chevrons + file
icons, doc-path + save-status in the editor, catalog tags and
no-results treatment in search results.
Also adds .gitignore (venv/node_modules/dist/pycache) and commits the
frontend package-lock.json that was previously untracked.
