refactor(app): introduce attachment storage layer and draft lifecycle management

Replace inline data-URL image handling with a persistent attachment storage service, add draft lifecycle states (active/abandoned/sent) with generation tracking, and update fetchAgent to return project placement alongside agent snapshots.

packages/app/src/utils/encode-images.ts

@@ -1,68 +1,10 @@
-import { Platform } from "react-native";
-import { File } from "expo-file-system";
+import type { AttachmentMetadata } from "@/attachments/types";
+import { encodeAttachmentsForSend } from "@/attachments/service";
 
-type ImageInput = { uri: string; mimeType?: string };
+type ImageInput = AttachmentMetadata;
 
 export async function encodeImages(
   images?: ImageInput[]
 ): Promise<Array<{ data: string; mimeType: string }> | undefined> {
-  if (!images || images.length === 0) {
-    return undefined;
-  }
-
-  const encodedImages = await Promise.all(
-    images.map(async ({ uri, mimeType }) => {
-      try {
-        const data = await (async () => {
-          if (Platform.OS === "web") {
-            if (uri.startsWith("data:")) {
-              const [, base64] = uri.split(",", 2);
-              if (!base64) {
-                throw new Error("Malformed data URI for image.");
-              }
-              return base64;
-            }
-            const response = await fetch(uri);
-            const blob = await response.blob();
-            const base64 = await new Promise<string>((resolve, reject) => {
-              const reader = new FileReader();
-              reader.onload = () => {
-                if (typeof reader.result !== "string") {
-                  reject(new Error("Unexpected FileReader result type."));
-                  return;
-                }
-                const [, resultBase64] = reader.result.split(",", 2);
-                if (!resultBase64) {
-                  reject(new Error("Failed to read image data as base64."));
-                  return;
-                }
-                resolve(resultBase64);
-              };
-              reader.onerror = () => {
-                reject(reader.error ?? new Error("Failed to read image data."));
-              };
-              reader.readAsDataURL(blob);
-            });
-            return base64;
-          }
-
-          const file = new File(uri);
-          return await file.base64();
-        })();
-
-        return {
-          data,
-          mimeType: mimeType ?? "image/jpeg",
-        };
-      } catch (error) {
-        console.error("[encodeImages] Failed to convert image:", error);
-        return null;
-      }
-    })
-  );
-
-  const validImages = encodedImages.filter(
-    (entry): entry is { data: string; mimeType: string } => entry !== null
-  );
-  return validImages.length > 0 ? validImages : undefined;
+  return await encodeAttachmentsForSend(images);
 }