ci: add TypeScript typecheck workflow

[saurabhhhcodes]

Closes #36

Summary

• add a dedicated npm run typecheck script using tsc --noEmit
• add a pull-request TypeScript Checks workflow that runs npm ci, typecheck, build, and declaration-output verification
• verify generated .d.ts files are present and non-empty after build

Validation

• npm ci
• npm run typecheck
• npm run build
• test -s dist/index.d.ts
• declaration file empty-check command from the workflow
• git diff --check

[saurabhhhcodes]

Quick scoring-label request: this PR closes GSSoC issue #36, which is labeled gssoc'26, level1, and feature: smart-routing. Could you please mirror the applicable GSSoC/difficulty/type labels onto the PR before merge?