feat: Google Gemini image generation for project covers

Schema:
- SystemSettings: geminiApiKey, geminiModel, imageProvider fields
- imageProvider: "dalle" (default) or "gemini"

Gemini Client (packages/api/src/gemini-client.ts):
- Direct HTTP call to Gemini REST API with responseModalities: [TEXT, IMAGE]
- Returns base64 data URL
- Error parsing with user-friendly messages

Router (project.ts):
- generateCover: routes to DALL-E or Gemini based on imageProvider setting
- New isImageGenConfigured query returning { configured, provider }

Admin UI (SystemSettingsClient.tsx):
- "Image Generation" section with provider radio buttons (DALL-E / Gemini)
- Conditional fields: DALL-E config or Gemini API key + model
- Separate save button for image settings

Security:
- geminiApiKey sanitized in audit logs (SENSITIVE_FIELDS)
- API key stored server-side only, never sent to client

Co-Authored-By: claude-flow <ruv@ruv.net>

apps/web/src/components/projects/CoverArtSection.tsx

@@ -25,7 +25,7 @@ export function CoverArtSection({ projectId, coverImageUrl, coverFocusY = 50, pr
   const fileInputRef = useRef<HTMLInputElement>(null);
   const utils = trpc.useUtils();
 
-  const { data: dalleStatus } = trpc.project.isDalleConfigured.useQuery();
+  const { data: imageGenStatus } = trpc.project.isImageGenConfigured.useQuery();
   const generateMutation = trpc.project.generateCover.useMutation();
   const uploadMutation = trpc.project.uploadCover.useMutation();
   const removeMutation = trpc.project.removeCover.useMutation();
@@ -207,7 +207,7 @@ export function CoverArtSection({ projectId, coverImageUrl, coverFocusY = 50, pr
           )}
 
           {/* Generate with AI */}
-          {dalleStatus?.configured && (
+          {imageGenStatus?.configured && (
             <button
               type="button"
               onClick={() => {