Defer TypeScript 7 upgrade until Next.js supports it

[tnunamak]

Dependabot PR #23 bumps typescript 6→7. Blocked upstream, not mergeable yet.

TypeScript 7.0.2 (the native/Corsa rewrite) deleted lib/typescript.js and locked down its package.json exports (only ., ./unstable/*, ./package.json). Next.js's internal dependency-checker cannot resolve the new package layout, so next build fails deterministically.

• TS 7 itself typechecks clean (reference-implementation + apps/console).
• validate web / validate railway-core fail because they run the console next build, which breaks on the TS 7 package layout.

No Next.js release supports TS 7 yet. Revisit when Next.js ships TS 7 compat. Keep TypeScript at ^6.x until then.

[tnunamak]

Update: not deferring after all. Next PR #95639 (useTypeScriptCli) merged 2026-07-10 and ships in next@16.3.0-canary.93. Moving to the Next 16.3 canary + TS 7 with experimental.useTypeScriptCli: true to unblock the build now (owner's call to run canary deliberately). PR incoming; will close this issue when it lands green.