T2 · Migrate SPC charts #182

Summary

Migrate the SPC control charts (X̄-R, I-MR, c-chart with Western Electric / Nelson overlays, plus the Week-10 EWMA/CUSUM depth) from Streamlit to the Next.js app, consuming the API delivered in P3.

Mostly stateless compute→render. The rule-overlay rendering is the interesting part; the disturbance simulator needs a client-side state model.

Part of P4 · Tool migration. Needs P2 (web foundation) and P3 (API). Strangler fig: Streamlit keeps serving every tool not yet migrated.

Scope

• React view(s) under web/app/app/, calling the P3 endpoints.
• Client-side state only — session state lives in React, there is no server-side session.
• Plotly figures render via the existing framework-agnostic figure builders (react-plotly.js); the chart layer is a host swap, not a rewrite.
• Loading and error states for every API call — this is where API cold start becomes a UX concern rather than an availability one.
• Delete the corresponding Streamlit page in this same issue, once parity is verified.

Constraints

• Session-state sites to re-implement: 2 (docs/research/frontend-migration.md §3.3).
• Exact endpoint names bind at execution time against the API actually delivered in P3 — do not assume names from the plan doc.
• Do not touch quality_core or engine logic. Presentation + transport only.
• Parity is measured on numbers, not layout: same input must produce identical results to the Streamlit page it replaces.

Definition of Done

• View live in the web app, wired to the P3 endpoints
• Parity verified against the Streamlit page on the same input — outputs identical
• Loading + error states implemented
• Streamlit page for this tool deleted; nav updated; remaining Streamlit tools still work
• web-gate and gate both green; zero diff to engines
• SME verification
• Definition of Done (📌 Definition of Done — the contract (read before every issue) #43) honored

Refs: epic #107, docs/research/web-platform-migration.md §5.2, docs/research/frontend-migration.md §3.3