Add landing page with horizontal rail design

[hrshl4codes]

Summary

• Adds a full-screen dark ambient landing page (LandingView.jsx + LandingView.css)
• Short horizontal SVG rail lines at screen edges with station nodes (Parser, Embeddings, Retrieval, Citations) — circle beads sit on the rails
• Sage-green radial glow top-right, grain noise overlay, Syne/DM Sans typography
• Animated bar visualizer, scroll indicator, tech strip (OpenAI, Cohere, Pinecone, FastAPI, React, Render)
• Updates App.js to start on the landing view and transition to upload on CTA click

Test plan

• Open http://localhost:3001 — landing page renders with dark background and 4 station labels
• Four faint horizontal rails visible at left and right screen edges
• Station circles appear on top of the rail lines (bead-on-wire effect)
• "Open App →" CTA transitions to the upload view
• "View on GitHub" opens the repo in a new tab
• Bar breathe animation plays continuously