Replace hand-written .d.ts with JSDoc + tsc auto-generation

- Delete hand-written index.d.ts that drifted from source
- Add JSDoc type annotations to all source files
- Create src/types.js with shared typedefs (SelfInfo, Contact,
  ContactMessage, ChannelInfo, RepeaterStats, etc.)
- Add tsconfig.json for declaration generation
- Add build:types script and prepublishOnly hook
- Add GitHub Actions CI workflow for type checking
- Use Uint8Array everywhere (no Buffer references)
- Add semantic type aliases (EpochSeconds, Milliseconds, MilliVolts)
- Add typed event overloads on Connection (on/once/off)
- All 11 PR #15 review comments addressed

src/random_utils.js

@@ -1,5 +1,10 @@
 class RandomUtils {
 
+    /**
+     * @param {number} min
+     * @param {number} max
+     * @returns {number}
+     */
     static getRandomInt(min, max) {
         min = Math.ceil(min);
         max = Math.floor(max);