Rebuild homepage as SaaS product entry

[mattyu-dev]

Outcome

• promote the complete product narrative to the canonical homepage
• remove the old secondary route and its historical artifacts
• reframe the public story as a real SaaS with a cold-neutral Geist and coral system
• rename active portfolio internals and QA evidence around the product

Verification

• 64 tests, Ruff and mypy pass
• browser QA passes on 7 viewports plus 320 px and 200% text resize
• Lighthouse accessibility 100/100 for product and workspace on desktop and mobile
• performance 90 desktop and 100 mobile, LCP below 1.9 s, CLS and TBT at 0
• npm and Python dependency audits report no known vulnerabilities
• the removed URL is verified as a 404