[Pepps233]

Summary

Adopt stable TypeScript 7 and current Biome tooling.

Reasoning

Use the stable native compiler for root validation while keeping existing preview tooling available to workspace build scripts. Migrate policy checks rather than retaining an old compiler API or weakening lint rules.

Changes

• Pin TypeScript 7.0.2, Biome 2.6.3, esbuild 0.28.2, tsx 4.23.15, and rimraf override 6.1.3.
• Use stable tsc in the root check and ES2024 target/lib, matching Unicode-set regex features already used on supported Node runtimes.
• Migrate the relative-import checker to TypeScript's exported native AST API, retaining all import forms, exclusions, and exact line/column diagnostics with isolated fixture coverage and deterministic cleanup.
• Migrate Biome schema/preset, satisfy new lint/format/export-order diagnostics, and preserve explicit false constrained-sampling semantics.
• Remove obsolete @types/diff stub; diff already provides declarations.
• Document compiler/tooling constraints. Native AST API paths are unstable and coupled to the exact compiler pin; native-preview itself has no stable release and was not updated to another prerelease.

Testing

• npm run check passed, including stable TypeScript and browser smoke.
• ./test.sh passed with isolated credentials.
• All modified actual test files were run directly; credential-dependent E2E cases skipped.
• Native import-check fixtures: 3 passed; constrained-sampling tests: 4 passed.
• Offline, isolated-home TUI smoke: startup and Settings dialog rendered successfully; no prompts or provider calls submitted.