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/@smithy/util-config-provider/dist-cjs/index.js

@@ -1,30 +0,0 @@
-'use strict';
-
-const booleanSelector = (obj, key, type) => {
-    if (!(key in obj))
-        return undefined;
-    if (obj[key] === "true")
-        return true;
-    if (obj[key] === "false")
-        return false;
-    throw new Error(`Cannot load ${type} "${key}". Expected "true" or "false", got ${obj[key]}.`);
-};
-
-const numberSelector = (obj, key, type) => {
-    if (!(key in obj))
-        return undefined;
-    const numberValue = parseInt(obj[key], 10);
-    if (Number.isNaN(numberValue)) {
-        throw new TypeError(`Cannot load ${type} '${key}'. Expected number, got '${obj[key]}'.`);
-    }
-    return numberValue;
-};
-
-exports.SelectorType = void 0;
-(function (SelectorType) {
-    SelectorType["ENV"] = "env";
-    SelectorType["CONFIG"] = "shared config entry";
-})(exports.SelectorType || (exports.SelectorType = {}));
-
-exports.booleanSelector = booleanSelector;
-exports.numberSelector = numberSelector;