feat(chat): #155 paste image depuis presse-papier dans le composer custom (QA verte)

- frontend: onPaste sur CustomAgentChatView, détection MIME image, chip/preview d'attachment, envoi via le contrat #154 (adapters/agent, ports)

- backend: import d'image par bytes dans le store attachments (commands, chat_attachments app+infra, dto, ports) + tests

frontend/src/features/agents/CustomAgentChatView.test.tsx

@@ -205,6 +205,159 @@ describe("CustomAgentChatView", () => {
     expect(screen.getAllByText("hello agent")).toHaveLength(1);
   });
 
+  it("pastes a clipboard image as a removable preview chip", async () => {
+    const agent = {
+      launchAgentChat: vi.fn(),
+      reattachAgentChat: vi.fn(async (sessionId: string) => ({
+        sessionId,
+        scrollback: [],
+      })),
+      sendAgentChat: vi.fn(() => new Promise<void>(() => {})),
+      cancelAgentChat: vi.fn(async () => {}),
+      closeAgentChat: vi.fn(async () => {}),
+    };
+
+    render(
+      <DIProvider
+        gateways={{
+          agent,
+          system: { pickFile: vi.fn(async () => null) },
+        } as unknown as Gateways}
+      >
+        <CustomAgentChatView
+          projectId="project-1"
+          agentId="agent-1"
+          agentName="Worker"
+          profile={profile}
+          cwd="/repo"
+          nodeId="node-1"
+          sessionId="chat-session-1"
+          conversationId="conversation-1"
+          onSessionId={vi.fn()}
+          onConversationId={vi.fn()}
+        />
+      </DIProvider>,
+    );
+
+    await waitFor(() =>
+      expect(agent.reattachAgentChat).toHaveBeenCalledWith(
+        "chat-session-1",
+        expect.any(Function),
+      ),
+    );
+
+    const file = new File(["ignored"], "clipboard.png", { type: "image/png" });
+    Object.defineProperty(file, "arrayBuffer", {
+      value: vi.fn(async () => new Uint8Array([1, 2, 3]).buffer),
+    });
+    fireEvent.paste(screen.getByLabelText(/message CLI custom/), {
+      clipboardData: {
+        items: [
+          {
+            kind: "file",
+            type: "image/png",
+            getAsFile: () => file,
+          },
+        ],
+        getData: () => "",
+      },
+    });
+
+    expect(await screen.findByText("Fichier joint: clipboard.png")).toBeTruthy();
+    expect(screen.getByTestId("attachment-preview-clipboard.png")).toBeTruthy();
+
+    fireEvent.click(screen.getByRole("button", { name: "retirer clipboard.png" }));
+
+    await waitFor(() =>
+      expect(screen.queryByText("Fichier joint: clipboard.png")).toBeNull(),
+    );
+    expect(
+      (screen.getByRole("button", { name: "Envoyer" }) as HTMLButtonElement)
+        .disabled,
+    ).toBe(true);
+  });
+
+  it("sends a pasted clipboard image without requiring text", async () => {
+    const agent = {
+      launchAgentChat: vi.fn(),
+      reattachAgentChat: vi.fn(async (sessionId: string) => ({
+        sessionId,
+        scrollback: [],
+      })),
+      sendAgentChat: vi.fn(async () => {}),
+      cancelAgentChat: vi.fn(async () => {}),
+      closeAgentChat: vi.fn(async () => {}),
+    };
+
+    render(
+      <DIProvider
+        gateways={{
+          agent,
+          system: { pickFile: vi.fn(async () => null) },
+        } as unknown as Gateways}
+      >
+        <CustomAgentChatView
+          projectId="project-1"
+          agentId="agent-1"
+          agentName="Worker"
+          profile={profile}
+          cwd="/repo"
+          nodeId="node-1"
+          sessionId="chat-session-1"
+          conversationId="conversation-1"
+          onSessionId={vi.fn()}
+          onConversationId={vi.fn()}
+        />
+      </DIProvider>,
+    );
+
+    await waitFor(() =>
+      expect(agent.reattachAgentChat).toHaveBeenCalledWith(
+        "chat-session-1",
+        expect.any(Function),
+      ),
+    );
+
+    const file = new File(["ignored"], "paste-image.png", { type: "image/png" });
+    Object.defineProperty(file, "arrayBuffer", {
+      value: vi.fn(async () => new Uint8Array([1, 2, 3]).buffer),
+    });
+    fireEvent.paste(screen.getByLabelText(/message CLI custom/), {
+      clipboardData: {
+        items: [
+          {
+            kind: "file",
+            type: "image/png",
+            getAsFile: () => file,
+          },
+        ],
+        getData: () => "",
+      },
+    });
+
+    await screen.findByText("Fichier joint: paste-image.png");
+    fireEvent.click(screen.getByRole("button", { name: "Envoyer" }));
+
+    await waitFor(() => expect(agent.sendAgentChat).toHaveBeenCalledTimes(1));
+    expect(agent.sendAgentChat).toHaveBeenCalledWith(
+      "chat-session-1",
+      "",
+      expect.any(Function),
+      {
+        attachments: [
+          {
+            filename: "paste-image.png",
+            contentBase64: "AQID",
+            mime: "image/png",
+            sourceKind: "clipboard",
+          },
+        ],
+      },
+    );
+    expect(screen.getByText("Pièce jointe")).toBeTruthy();
+    expect(screen.getByText("Fichier: paste-image.png")).toBeTruthy();
+  });
+
   it("keeps the chat shell bounded with a scrollable message area and fixed composer", async () => {
     const agent = {
       launchAgentChat: vi.fn(() => new Promise<never>(() => {})),