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

tsconfig.json

@@ -0,0 +1,16 @@
+{
+  "include": ["src/**/*.js"],
+  "compilerOptions": {
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "declarationMap": true,
+    "outDir": "dist",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "target": "ESNext",
+    "strict": false,
+    "skipLibCheck": true
+  }
+}