build: Bump TypeScript 5.9.3 to ^6.0.3

[facioquobo]

Summary

• Bump typescript from 5.9.3 to ^6.0.3 (latest stable).
• Pre-implementation review: confirmed no in-flight PR or existing work touches this dependency (0 open PRs on this repo at time of writing); this is a standalone dependency-currency bump.
• TypeScript 6.0 changes the default types compiler option from implicitly including every package under node_modules/@types to an empty array (release notes). This repo's root tsconfig.json relied on the old implicit behavior to resolve ambient Node globals (Buffer, process) for playwright.config.ts and other Node-context files reachable from the default program, which surfaced ~60 new TS2591/TS2550 errors under 6.0. Fixed by explicitly setting "types": ["node"] on the root config; tsconfig.app.json (browser build) and tsconfig.spec.json (test build) already declare their own types arrays and are unaffected.
• @angular/build@21.2.x declares a peer dependency of typescript >=5.9 <6.0, narrower than @angular/compiler-cli's >=5.9 <6.1. npm install surfaces this as an ERESOLVE overriding peer dependency warning (not a hard failure). Angular's own build tooling does not officially support TypeScript 6.0 until @angular/build@22.x, which requires bumping @angular/core to ^22.0.0 — out of scope for this dependency-only bump. Flagging this for awareness; lint/typecheck/build all pass clean against 6.0.3 in the meantime.

Test plan

Ran locally against TypeScript 6.0.3:

• npm run lint — pass (markdownlint, eslint, prettier all clean)
• npm run typecheck — pass (zero errors after the tsconfig.json fix above; confirmed the errors were absent under the previous 5.9.3 pin and only appear under 6.0.3, isolating the regression to the TS6 types default change)
• npm run build — pass (ng build --configuration=development completes, bundle output unchanged in shape)
• npm test (Vitest) — could not complete a full run in this environment due to sandbox memory limits (Angular + jsdom + Vite transform is memory-heavy); a reduced-scope run confirmed the Angular TestBed and spec files execute correctly under TS 6.0.3. CI (ubuntu-latest, ample memory) will run the full npm run test:coverage and npm run e2e suites as part of this PR's checks — please treat those as the authoritative test signal.

Requesting facioquo/org-reviewers for review.

[facioquobo]

Converting back to draft: CI's `npm ci` step fails with a hard `ERESOLVE` error that my local `npm install` masked with an override warning.

Root cause: `@angular/build@21.2.13` declares `peerDependencies.typescript: ">=5.9 <6.0"`. This is Angular's own compatibility ceiling, not incidental — checked every 21.2.x patch (13 through 18) and all cap at `<6.0`. Full TypeScript 6.0 support only ships in `@angular/build@22.x`, which requires `@angular/core@^22.0.0` (a major Angular upgrade, out of scope for a dependency-only bump).

`npm install` resolves this leniently with a warning and overrides the conflict, so lint/typecheck/build all pass locally against 6.0.3 — but `npm ci` (used in CI, and the correct tool for reproducible installs) refuses to install at all under this conflict.

Holding this in draft pending a decision on how to proceed (e.g. wait for an Angular 21.x patch that raises the ceiling, or explicitly accept the unsupported-by-Angular combination via a package.json `overrides` entry).

[facioquobo]

Blocked: TypeScript 6 is incompatible with the pinned Angular build toolchain here

CI's lint-and-test job fails on npm ci with an ERESOLVE error: @angular/build@21.2.13 declares peerDependencies.typescript: ">=5.9 <6.0". I checked every published 21.x release of @angular/build on npm (21.0.0 through the current 21.2.18) and all of them cap TypeScript below 6.0. The peer range only opens to >=6.0 <6.1 starting at @angular/build@22.0.0, which itself requires @angular/core@^22.0.0.

So this repo cannot adopt TypeScript 6 as a standalone dependency bump — it requires bumping Angular's core/build packages from 21.x to 22.x, a major framework version upgrade with its own migration surface, breaking changes, and risk profile. That's materially different from "single-dependency devDependency bump, no runtime/production code path affected," which is what this PR (and its Board pre-approval) was scoped and assessed as.

Rather than forcing the install with --legacy-peer-deps/an overrides entry (which would silence a real, unvalidated incompatibility Angular's own maintainers haven't signed off on), I'm closing this PR without merging. TypeScript 6 adoption for this repo needs to be planned and approved as part of an Angular 21 -> 22 upgrade, tracked separately with its own scope and risk assessment.

No code in this PR is unsafe; it's simply not completable as scoped. Local npm install masked this because npm's non-ci install path auto-resolves peer conflicts with a warning instead of failing, which is why it wasn't caught before pushing.

[facioquobo]

Closing per the finding above: not completable as scoped without a major Angular 21->22 bump. Will reopen tracked as part of that larger migration once planned/approved.