feat: add save_image tool and list image MCP tools

Expose save_image across direct model, MCP gateway, DeepSeek Harness and remote Agents (written on the remote host via chunked reads), and show the image MCP tool list in settings.

src/main/agent/image-tool-binding.ts

@@ -1,10 +1,20 @@
 import { z } from 'zod'
-import { imageToolInputSchema, imageToolName, type ImageOperation, type ImageRequestContext } from '../../shared/image-generation-contracts'
+import {
+  imageSaveToolDescription, imageSaveToolInputSchema, imageSaveToolName,
+  imageToolInputSchema, imageToolName,
+  type ImageOperation, type ImageRequestContext, type ImageSaveResult
+} from '../../shared/image-generation-contracts'
 
 export type ImageToolBinding = {
   context: Readonly<ImageRequestContext>
   describe(): Promise<string | undefined>
   call(input: unknown, callId: string, waitSignal?: AbortSignal): Promise<ImageOperation>
+  /** Writes an existing conversation image to a local file. Absent for bindings without local file access. */
+  save?(input: unknown, signal?: AbortSignal): Promise<ImageSaveResult>
+  /** Returns image bytes in the requested format so a remote Agent can write them on its own host. */
+  readForSave?(artifactId: string, mimeType: ImageSaveResult['mimeType']): Promise<Buffer>
+  /** save_image description with this conversation's image IDs; undefined when saving is not meaningful. */
+  describeSave?(): Promise<string | undefined>
 }
 
 export async function imageToolDefinition(binding: ImageToolBinding | undefined) {
@@ -14,3 +24,12 @@ export async function imageToolDefinition(binding: ImageToolBinding | undefined)
   Reflect.deleteProperty(inputSchema, '$schema')
   return { name: imageToolName, displayName: 'Generate or edit image', description, inputSchema, source: 'builtin' as const }
 }
+
+export async function imageSaveToolDefinition(binding: ImageToolBinding | undefined) {
+  if (!binding?.save || binding.context.workMode !== 'execute') return undefined
+  const description = binding.describeSave ? await binding.describeSave() : imageSaveToolDescription
+  if (!description) return undefined
+  const inputSchema = z.toJSONSchema(imageSaveToolInputSchema, { target: 'draft-7', io: 'input' })
+  Reflect.deleteProperty(inputSchema, '$schema')
+  return { name: imageSaveToolName, displayName: 'Save image to file', description, inputSchema, source: 'builtin' as const }
+}