Modernize frontend foundations and tooling

[dimaip]

Stack

This is PR 1 of 3. Merge the stack from the bottom up.

1. Frontend foundations and tooling — this PR
2. Frontend runtime and service performance — #734
3. Performance measurement and evidence harness — #735

What changed

• Pins the supported frontend runtime to Node 24.18 and Yarn 1.22.
• Upgrades the React, router, query, MUI/Emotion, TypeScript, ESLint, Babel, Webpack, and test toolchain.
• Migrates the application to React 18 and modern router/query APIs.
• Adds strict quality ratchets so existing lint and type debt cannot grow.
• Adds browser E2E coverage, bundle reporting, Node 24 CI, and reproducible production-build checks.
• Removes obsolete browser polyfills and legacy runtime packages.
• Documents the modernization backlog, architecture boundaries, regression strategy, and offline constraints.

Why

The frontend had accumulated nearly a decade of dependency, build, typing, and architecture debt. This establishes a supported, measurable baseline before further performance work, without attempting a backend rewrite.

Impact and constraints

• Backend/PHP is untouched.
• Capacitor and TWA upgrade work remains deferred.
• The service-worker strategy and activation behavior are preserved.
• Dynamic MDX, installed/offline behavior, and custom UI controls remain supported.
• No speculative replacement of custom controls with native select elements is included.

Validation

Implementation was exercised through frontend unit tests, quality ratchets, production builds, bundle reports, and browser E2E smoke coverage. Later PRs in the stack add the full service and installed-performance evidence harness.

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Project	Deployment	Actions	Updated (UTC)
calendar	Ready	Preview	Aug 6, 2026 2:17pm