add .gitignore, clean up generated files from node_modules

Remove from tracking:
- dist/ (build output, regenerated by bun run build.ts)
- node_modules/.pnpm/ (pnpm internal store, 247MB)
- node_modules/.bin/ (executable symlinks)
- node_modules/.ignored/ and .ignored_* (source-map dirs moved aside by pnpm)
- 100 pnpm-installed package symlinks (regenerated by pnpm install)

Keep in tracking:
- Private package stubs not on npm (color-diff-napi, modifiers-napi,
  @ant/claude-for-chrome-mcp, @anthropic-ai/mcpb, @anthropic-ai/sandbox-runtime)
- Source-map extracted packages not installed by pnpm (@grpc/*, @protobufjs/*, etc.)

claude-code-source/node_modules/@aws-crypto/util/build/uint32ArrayFrom.js

@@ -1,20 +0,0 @@
-"use strict";
-// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
-// SPDX-License-Identifier: Apache-2.0
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.uint32ArrayFrom = void 0;
-// IE 11 does not support Array.from, so we do it manually
-function uint32ArrayFrom(a_lookUpTable) {
-    if (!Uint32Array.from) {
-        var return_array = new Uint32Array(a_lookUpTable.length);
-        var a_index = 0;
-        while (a_index < a_lookUpTable.length) {
-            return_array[a_index] = a_lookUpTable[a_index];
-            a_index += 1;
-        }
-        return return_array;
-    }
-    return Uint32Array.from(a_lookUpTable);
-}
-exports.uint32ArrayFrom = uint32ArrayFrom;
-//# sourceMappingURL=uint32ArrayFrom.js.map