feat: add storage system with local disk and S3 providers

Introduces a provider-agnostic storage subsystem for file attachments.
Includes local disk and S3 backends, asset/attachment DB schemas, issue
attachment CRUD routes with multer upload, CLI configure/doctor/env
integration, and enriched issue ancestors with project/goal resolution.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/home-paths.ts

@@ -44,6 +44,10 @@ export function resolveDefaultSecretsKeyFilePath(): string {
   return path.resolve(resolvePaperclipInstanceRoot(), "secrets", "master.key");
 }
 
+export function resolveDefaultStorageDir(): string {
+  return path.resolve(resolvePaperclipInstanceRoot(), "data", "storage");
+}
+
 export function resolveHomeAwarePath(value: string): string {
   return path.resolve(expandHomePrefix(value));
 }