Port phase 1 to TypeScript

Move the standalone GameSense scale lighting to TypeScript ahead of the
Max for Live work, so step 3 gets type declarations at the seam.

Build emits CommonJS at ES2020 into dist/, because Node for Max loads CJS
on a Node version we do not control. bin/apex7-scale.js becomes a plain-JS
launcher so `node bin/apex7-scale.js` keeps working; the CLI itself moves
to src/cli.ts.

Two modules make previously implicit structure explicit:

  - src/protocol.ts, the GameSense wire types, so the transport and the
    payload construction agree on shapes neither of them owns
  - src/errors.ts, since `catch (err)` binds `unknown` under strict

Typing surfaced a few real fixes:

  - ScaleLighting.started was a public field the CLI set by hand to make
    --off work without start(); that is now release(), with started
    private behind isStarted
  - readAddress() trusted JSON.parse output; the address is now checked
    for being a non-empty string
  - res.statusCode is number|undefined, so the old `>= 200` comparison
    coerced silently; a missing status now rejects
  - parseIntervals claimed to dedupe and sort, and never did (comment
    corrected; pitchClassesFor is what dedupes)

Behavior is otherwise unchanged: all 18 tests pass and --once, --off,
--demo, --key-test, the resident stdin loop and the error paths were
verified against tools/fake-gamesense.ts.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

package.json

@@ -2,18 +2,30 @@
   "name": "steelseries-live-scale",
   "version": "0.1.0",
   "description": "Highlight the notes of the current Ableton Live scale on a SteelSeries Apex 7 via GameSense",
-  "main": "src/index.js",
+  "main": "dist/src/index.js",
+  "types": "dist/src/index.d.ts",
   "bin": {
     "apex7-scale": "bin/apex7-scale.js"
   },
+  "files": [
+    "bin",
+    "dist/src"
+  ],
   "scripts": {
-    "start": "node bin/apex7-scale.js",
-    "stub": "node tools/fake-gamesense.js",
-    "test": "node test/logic.test.js"
+    "build": "tsc",
+    "typecheck": "tsc --noEmit",
+    "prepare": "npm run build",
+    "start": "npm run build && node bin/apex7-scale.js",
+    "stub": "npm run build && node dist/tools/fake-gamesense.js",
+    "test": "npm run build && node dist/test/logic.test.js"
   },
   "engines": {
-    "node": ">=14"
+    "node": ">=16"
   },
   "license": "MIT",
-  "private": true
+  "private": true,
+  "devDependencies": {
+    "@types/node": "^26.2.0",
+    "typescript": "^7.0.2"
+  }
 }