Lighthouse Perf

Configures Lighthouse CI (`@lhci/cli`) to audit Web Vitals (LCP, INP, CLS) on every PR, asserts against canonical thresholds (LCP ≤2.5s, INP ≤200ms, CLS ≤0.1 at the 75th percentile), uploads Lighthouse reports as build artifacts, and posts deltas as PR comments. Includes a budget-authoring reference: per-route LCP/INP/CLS thresholds by traffic class (cached / dynamic / api-heavy / form-heavy / media-heavy) via `assertMatrix`, plus `budget.json` resource-size caps (JS / CSS / images / total bytes). Use when the project ships a web frontend and the team needs continuous Web Vitals monitoring tied to PR gating, or needs its first Lighthouse budgets drafted.