feat: Image Upload, Design Systems, and Test Hardening

[davideast]

This PR introduces several handwritten extensions to the Stitch SDK to support advanced workflows, along with test suite hardening:

1. Direct Image Upload: Support for uploading images directly to the Stitch API via Project.uploadImage (using private REST endpoints not exposed in MCP).
2. Design System Utilities: Handwritten helpers on Project to infer themes from HTML, sync themes to the API, and inject them into prompts.
3. Asset Downloader: A robust Project.downloadAssets method that localizes screen assets and prevents ENAMETOOLONG errors.
4. Test Suite Hardening: Resolves a critical data leak in test mocks and removes all as any assertions in key test files.
5. Workflow Cleanup: Removes deprecated Fleet workflows, leaving only the core CI pipeline.

Usage

Image Upload & Theme Extraction Flow

import { stitch } from "@google/stitch-sdk";
import * as fs from "fs/promises";

const project = stitch.project("4044680601076201931");

// 1. Upload an image
const [screen] = await project.uploadImage("path/to/mockup.png", {
  title: "Source Mockup"
});

// 2. Infer theme from the generated HTML
const theme = await project.inferTheme(screen.id);

// 3. Sync inferred theme to the project's design system
await project.syncTheme(theme);

// 4. Guide future generations with this theme
const prompted = project.themePrompt("Create a login page", theme);

Asset Downloader

// Download all screens and assets to a local folder
await project.downloadAssets("./dist/preview");

Changes

Image Upload

• Project.uploadImage — Handwritten method for direct REST upload of image assets (PNG, JPEG, WebP), returning domain Screen objects.
• upload-handler.ts — Internal handler for managing multipart uploads and resolving correct endpoints.

Design System Utilities (Handwritten)

• Project.inferTheme(screenId) — Parses HTML of a screen to extract theme tokens (customColor, headlineFont, roundness) using a rule-based extraction system.
• Project.syncTheme(theme) — Orchestrates the API dance to either create or update the project's design system with the inferred theme.
• Project.themePrompt(prompt, theme) — Injects design system tokens into a text prompt to guide future generations.

Asset Downloader

• Project.downloadAssets(outputDir) — Downloads all screens and their referenced assets, rewriting URLs to be self-contained.
• Path Length Safety — Truncates base encoded filenames to 100 chars to prevent ENAMETOOLONG errors on deep paths.

Test Suite & Hardening

• Data Leak Fix — Fixed a mock leak in theme-extensions.test.ts where using .buffer exposed the Node.js shared pool. Now uses clean manual ArrayBuffer construction.
• Type Safety — Removed manual as any casts in tests and resolved all type errors in theme-extensions.test.ts.
• Workflows — Removed fleet-analyze.yml, fleet-dispatch.yml, fleet-label.yml, fleet-merge.yml, and jules-merge-conflicts.yml. Only ci.yml remains.