fix: correct package entry points and publish contents

Five packaging defects, all pre-existing:

1. dist/esm/index.js held ESM syntax while the package is not
   "type": "module", so Node classified it as CommonJS. It failed
   outright on Node 18 ("Unexpected token 'export'") and only worked on
   Node >= 22 because Node re-parses after guessing the module type,
   paying that cost on every import. Bundles now carry explicit
   extensions: .mjs for ES output, .cjs/.js for CommonJS. The browser
   build gained a real CommonJS output too — the exports map previously
   pointed the browser "require" condition at an ES module.
   The exports map now also leads with "types" and ends with a "default"
   fallback for resolvers matching neither "node" nor "browser".

2. files: ["native"] published the local build directory: a 94.6 kB
   Linux-x64 .node binary, a 148 kB object file and generated Makefiles.
   node-gyp-build checks build/Release before prebuilds, so every
   consumer on every platform would have found this machine's binary,
   skipped compiling, and failed to load it. It fails safe (native/
   index.js catches and returns null), but the addon could never work
   for anyone else. Narrowed to the four source files.

3. binding.gyp resolves node-addon-api at build time, but nothing
   declared it: it was a devDependency of the root, absent from
   native/package.json. The build only succeeded here because a dev
   install populates the root node_modules. Declared as a dependency of
   the native package, where it is actually needed.

4. No clean step, so stale output shipped — the tarball carried both
   dist/types/core/** and a dist/types/src/** tree left over from before
   rootDir was set. build now runs clean first.

5. test:browser ran `karma start` with no karma.conf.js anywhere in the
   repo, and tests/browser is an empty directory. Removed the script and
   the karma devDependency rather than leave a script that cannot run.

Verified: CommonJS require and ESM import both resolve on Node 18.19.1
and 24.18.0; TypeScript resolves types under both bundler and node16;
npm pack now produces 35 files / 103.8 kB with no build artefacts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package.json

@@ -3,35 +3,39 @@
     "version": "0.3.0",
     "description": "OpenAI-compatible secure chat client with end-to-end encryption",
     "main": "dist/node/index.js",
-    "browser": "dist/browser/index.js",
-    "module": "dist/esm/index.js",
+    "browser": "dist/browser/index.mjs",
+    "module": "dist/esm/index.mjs",
     "types": "dist/types/index.d.ts",
     "exports": {
         ".": {
-            "node": {
-                "require": "./dist/node/index.js",
-                "import": "./dist/esm/index.js"
-            },
+            "types": "./dist/types/index.d.ts",
             "browser": {
-                "import": "./dist/browser/index.js",
-                "require": "./dist/browser/index.js"
+                "import": "./dist/browser/index.mjs",
+                "require": "./dist/browser/index.cjs"
             },
-            "types": "./dist/types/index.d.ts"
+            "node": {
+                "import": "./dist/esm/index.mjs",
+                "require": "./dist/node/index.js"
+            },
+            "default": "./dist/browser/index.mjs"
         }
     },
     "files": [
         "dist",
-        "native",
+        "native/binding.gyp",
+        "native/index.js",
+        "native/package.json",
+        "native/src",
         "README.md",
         "LICENSE"
     ],
     "scripts": {
-        "build": "npm run build:node && npm run build:browser && npm run build:types",
+        "clean": "node -e \"require('fs').rmSync('dist',{recursive:true,force:true})\"",
+        "build": "npm run clean && npm run build:node && npm run build:browser && npm run build:types",
         "build:node": "rollup -c --environment TARGET:node",
         "build:browser": "rollup -c --environment TARGET:browser",
         "build:types": "tsc --emitDeclarationOnly",
         "test": "jest",
-        "test:browser": "karma start",
         "prepublishOnly": "npm run build && npm test"
     },
     "keywords": [
@@ -55,7 +59,6 @@
         "@types/jest": "^30.0.0",
         "@types/node": "^24.0.0",
         "jest": "^30.0.0",
-        "karma": "^6.4.0",
         "node-addon-api": "^8.6.0",
         "node-gyp": "^13.0.0",
         "node-gyp-build": "^4.8.0",