GET /data?from&to&step[&compare=1] and ?turn=<id> serve the facts as series for owner and moderators (src/data-series.ts, src/data-api.ts) #529

Second piece of #508. Take src/data-series.ts and src/data-api.ts from branch quill/508-a-data-view-to-explore-the-arm-people-pr (74967da).

Done when:

• [ ] src/data-series.ts cuts the facts into steps, and the top of the file says how each number is made. Sums are added before dividing. A step's p95 is the p95 of its turns' p95s. Uptime is live minutes over minutes passed.
• [ ] GET /data answers 403 to anonymous visitors and plain users and 200 to the owner and moderators. A bad parameter is a 400 that says what to send.
• [ ] data-series.test.ts and data-api.test.ts pass, and so does bun --cwd Software/so101 test.

Brief: any builder.