Add strict TypeScript type checking to build pipeline

[dollfins]

Description

The tsconfig.json has "strict": true but the build script (npm run compile) runs webpack directly without a separate type-check step. Webpack with ts-loader does not enforce strict type checking by default — it only transpiles. This means type errors can slip through.

Current State

// tsconfig.json has strict: true
// but compile runs: webpack --mode production
// which uses ts-loader without fork-ts-checker-webpack-plugin

Type errors that should be caught at build time are silently ignored.

Expected Behavior

Add a type-check step to the build process:

1. Install fork-ts-checker-webpack-plugin for in-bundle type checking, OR
2. Add a separate typecheck script: tsc --noEmit
3. Run type checking in CI and before publishing

The vscode:prepublish script should include type checking:

"vscode:prepublish": "npm run typecheck && npm run compile && npm run lint"

Acceptance Criteria

• npm run typecheck catches TypeScript strict mode errors
• Build fails when type errors are present
• CI workflow includes type-check step
• All existing code passes strict type checking (or has explicit type annotations added as needed)

Complexity

Trivial — adding a script and a devDependency, minor type fixes.

Points

100