fix: clean dist/ before build:ts in TypeScript template

[winnrz]

What

Adds a clean script to the generated TypeScript template and runs it before tsc in build:ts, so stale compiled files are removed on every build.

Why

Closes #878. Without this, deleting a file from routes/ or plugins/ leaves a stale .js in dist/, which @fastify/autoload continues to serve — giving the misleading impression that the deletion had no effect. This is a non-obvious debugging problem for developers new to Fastify.

Changes

• Added clean script using inline node -e (no new dependency, cross-platform)
• Updated build:ts to run clean first
• Added a logInstructions entry for clean so it's discoverable
• Fixed a pre-existing typo in logInstructions: npm build:ts → npm run build:ts

The ESM TypeScript template inherits from typescriptTemplate via spread in cli(), so both --lang=ts and --lang=ts --esm pick up the change.

Verification

Stale file removal on a generated project:

$ mkdir -p dist && echo "stale" > dist/stale.js
$ ls dist/
stale.js
$ npm run clean
$ ls dist/ 2>/dev/null || echo "dist/ removed"
dist/ removed

Tests pass locally:

• npm test passes end-to-end
• npm run unit:ts-cjs ✓
• npm run unit:ts-esm ✓

On Node 20 the template test suites are auto-skipped by the repo's should-skip-test-suites.js, but I ran unit:ts-cjs and unit:ts-esm directly and both pass.

Note

npm run build:ts currently fails on a freshly generated project due to an unrelated TS5011 rootDir error, which reproduces on main without this change. This PR does not affect that behavior — the clean step completes successfully before tsc is invoked.

Alternatives considered

• rimraf: adds a dependency for what's essentially a one-liner
• tsc --build --clean: requires incremental/project-reference builds, which the current template doesn't use

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin and the Code of conduct

Note on "tests and/or benchmarks are included": no new tests added because the change is to the generated scripts object, which isn't asserted on in the existing test suite. The existing TS template tests (unit:ts-cjs and unit:ts-esm) pass. Happy to add coverage if reviewers prefer.