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/@anthropic-ai/vertex-sdk/internal/headers.mjs

@@ -1,74 +0,0 @@
-// File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
-import { isReadonlyArray } from "./utils/values.mjs";
-const brand_privateNullableHeaders = Symbol.for('brand.privateNullableHeaders');
-function* iterateHeaders(headers) {
-    if (!headers)
-        return;
-    if (brand_privateNullableHeaders in headers) {
-        const { values, nulls } = headers;
-        yield* values.entries();
-        for (const name of nulls) {
-            yield [name, null];
-        }
-        return;
-    }
-    let shouldClear = false;
-    let iter;
-    if (headers instanceof Headers) {
-        iter = headers.entries();
-    }
-    else if (isReadonlyArray(headers)) {
-        iter = headers;
-    }
-    else {
-        shouldClear = true;
-        iter = Object.entries(headers ?? {});
-    }
-    for (let row of iter) {
-        const name = row[0];
-        if (typeof name !== 'string')
-            throw new TypeError('expected header name to be a string');
-        const values = isReadonlyArray(row[1]) ? row[1] : [row[1]];
-        let didClear = false;
-        for (const value of values) {
-            if (value === undefined)
-                continue;
-            // Objects keys always overwrite older headers, they never append.
-            // Yield a null to clear the header before adding the new values.
-            if (shouldClear && !didClear) {
-                didClear = true;
-                yield [name, null];
-            }
-            yield [name, value];
-        }
-    }
-}
-export const buildHeaders = (newHeaders) => {
-    const targetHeaders = new Headers();
-    const nullHeaders = new Set();
-    for (const headers of newHeaders) {
-        const seenHeaders = new Set();
-        for (const [name, value] of iterateHeaders(headers)) {
-            const lowerName = name.toLowerCase();
-            if (!seenHeaders.has(lowerName)) {
-                targetHeaders.delete(name);
-                seenHeaders.add(lowerName);
-            }
-            if (value === null) {
-                targetHeaders.delete(name);
-                nullHeaders.add(lowerName);
-            }
-            else {
-                targetHeaders.append(name, value);
-                nullHeaders.delete(lowerName);
-            }
-        }
-    }
-    return { [brand_privateNullableHeaders]: true, values: targetHeaders, nulls: nullHeaders };
-};
-export const isEmptyHeaders = (headers) => {
-    for (const _ of iterateHeaders(headers))
-        return false;
-    return true;
-};
-//# sourceMappingURL=headers.mjs.map