chore: Use symlinks for static assets served.

[jsantell]

Summary by cubic

Switched static assets to symlinks and updated copying to dereference them so builds include real files. Consolidated JSX type defs into a single source under @commontools/html to remove duplication.

• Refactors
  • Types now point to packages/html/src/jsx.d.ts; static/assets/types/jsx.d.ts is a symlink to that file.
  • Replaced @std/fs copy with a local helper in packages/deno-web-test/utils.ts that resolves symlinks and copies the target files/directories.

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