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-sdk/credential-providers/dist-cjs/index.js

@@ -1,20 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.fromHttp = void 0;
-const tslib_1 = require("tslib");
-tslib_1.__exportStar(require("./createCredentialChain"), exports);
-tslib_1.__exportStar(require("./fromCognitoIdentity"), exports);
-tslib_1.__exportStar(require("./fromCognitoIdentityPool"), exports);
-tslib_1.__exportStar(require("./fromContainerMetadata"), exports);
-tslib_1.__exportStar(require("./fromEnv"), exports);
-var credential_provider_http_1 = require("@aws-sdk/credential-provider-http");
-Object.defineProperty(exports, "fromHttp", { enumerable: true, get: function () { return credential_provider_http_1.fromHttp; } });
-tslib_1.__exportStar(require("./fromIni"), exports);
-tslib_1.__exportStar(require("./fromInstanceMetadata"), exports);
-tslib_1.__exportStar(require("./fromLoginCredentials"), exports);
-tslib_1.__exportStar(require("./fromNodeProviderChain"), exports);
-tslib_1.__exportStar(require("./fromProcess"), exports);
-tslib_1.__exportStar(require("./fromSSO"), exports);
-tslib_1.__exportStar(require("./fromTemporaryCredentials"), exports);
-tslib_1.__exportStar(require("./fromTokenFile"), exports);
-tslib_1.__exportStar(require("./fromWebToken"), exports);