feat(deps): react 19 + typescript 7 native (ts6 api side-by-side)

[PostboxRetinal]

Summary

Upgrade the core frontend toolchain to current stable: React 18 -> 19 and a TypeScript 7 (native Go compiler) build, keeping the programmatic TS 6 API side-by-side for lint tooling.

Changes

Package	From	To	Role
react / react-dom	^18.3.1	^19.0.0	React 19 (stable)
@types/react / @types/react-dom	^18.3.1	^19.0.0	React 19 types
typescript	~5.9.3	^6.0.2	TS 6 programmatic API (for typescript-eslint)
@typescript/native	(new)	npm:typescript@^7.0.2	Native tsc CLI (Go, 8-12x faster builds)

Why TS 6 + TS 7 side-by-side

• typescript-eslint requires the typescript peer as >=4.8.4 <6.1.0 and hard-crashes if it loads TS >= 7 (ts.versionMajorMinor guard at module load).
• The officially documented bridge npm:@typescript/typescript6 does not resolve correctly under bun 1.3.14 (see bun install misresolves a nested npm: alias to a different same-version package (breaks TypeScript 7 / @typescript/typescript6 coexistence) oven-sh/bun#33834): its internal @typescript/old alias misresolves to the bridge itself, leaving require('typescript') empty.
• Robust fix: pin the real typescript@6 for the API (ESLint) and @typescript/native for the CLI (build). bud resolves .bin/tsc -> native 7.0.2 and require('typescript') -> 6.0.3 API.

Verification

• bun install resolves clean
• bunx eslint . -> 0 errors
• bunx tsc --noEmit (native 7.0.2) -> exit 0
• bun run build (tsc -b && vite build) -> 43 modules, exit 0

Testing

Verified in feat/migration against current main. Manual smoke test of the core flow (auth -> record -> transcribe -> submit -> research EF -> citations) is still pending and tracked separately.

Rollback

Surgical, per-milestone:

• React: revert react* to ^18.3.1.
• TS: remove @typescript/native, restore typescript to ~5.9.3.