Rewrite landing page around explicit system meaning

[NickSeagull]

Summary

• reframe the landing page around the difference between generated code and explicit system meaning
• make requests, decisions, accepted facts, and useful views the central NeoHaskell model
• replace absolute correctness and effortless-scale claims with a clearer account of what people, compilers, tests, and AI agents each contribute
• update the site description to match the new positioning

Verification

• corepack yarn typecheck
• corepack yarn build
• git diff --check
• inspected the built landing page in Safari at normal zoom and an enlarged narrow-layout stress state

[NickSeagull]

Superseded by #30, which includes the expanded application-model visuals and page cleanup.