Remove vestigial FastAPI artifacts

[jeanclawd]

Problem

The repository still carries dead weight from its previous life as a FastAPI backend:

• `frontend/js/app.js` (around line 6) defines `const API_BASE = ''` which is never read — every call goes through `pyCall()`, not `fetch()`. `CLAUDE.md` already notes it as "vestigial leftover".
• Top-level `pyproject.toml` and `.python-version` exist with no functional role (`dependencies = []` per `CLAUDE.md`). They mislead newcomers into running `pip install` or assuming a server is involved.

Proposal

• Delete the `API_BASE` constant and any commented-out `fetch()` calls.
• Update README to state clearly: this is a 100% static site, no Python or Node toolchain needed to serve it.

Acceptance criteria

• No unused `API_BASE` symbol in the codebase.
• No empty Python project files at the root, or they carry an explanatory comment.
• README "Running locally" section makes the static-only nature explicit in the first paragraph.

Why now

5-minute fix. Reduces new-contributor confusion (no false "do I need a Python venv?" detour) and keeps the codebase honest.