Unify marketing locale routes

[visoar]

Summary

• Move public marketing pages into the single src/app/[locale] route tree and remove the duplicate (pages) implementation.
• Keep English bare URLs canonical by rewriting them internally to /en/... in src/proxy.ts; non-English bare marketing URLs still redirect to their locale prefix.
• Update static locale params, metadata alternates, route tests, Lingo cache, and path documentation.

Verification

• pnpm -s prettier:check
• pnpm -s lint
• pnpm -s type-check
• pnpm -s test
• LINGO_BUILD_MODE=cache-only pnpm -s build