feat(memos): include source_channel=email in memo inbox list

list 쿼리 확장:
- 기존 source_channel IN (memo, voice) → OR (source_channel = email AND source_external_id IS NOT NULL)
- mailplus_archive 의 INBOX root archive row (source_external_id=NULL) 는 자동 제외
- inbox_ingest 가 만든 email memo 만 /memos UI 에 노출

MemoResponse 확장:
- source_external_id: Message-ID 또는 imap UID fallback
- email_subject: email_metadata.subject (UI 부제/툴팁)

_to_memo_response 가 email_metadata JSONB 에서 subject 추출.

ingest 가 만든 row 가 UI 에 보이는 게 PR-2B 의 분류 배지/4 버튼/promote flow 자산 재사용의 전제.

plan: ~/.claude/plans/document-enchanted-candy.md

app/api/memos.py

@@ -15,7 +15,7 @@ from typing import Annotated, Any
 
 from fastapi import APIRouter, Depends, File, Form, HTTPException, Query, UploadFile
 from pydantic import BaseModel, Field
-from sqlalchemy import delete, func, select
+from sqlalchemy import delete, func, select, or_, and_
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from core.auth import get_current_user
@@ -178,6 +178,9 @@ class MemoResponse(BaseModel):
     source_channel: str | None = None  # voice/memo 등 진입점 식별 (UI 배지)
     file_type: str | None = None  # audio (voice 메모) vs note (text 메모)
     file_path: str | None = None  # voice 메모의 NAS audio 경로 (audio player 용)
+    # PR-4 Email Ingest — 이메일 source 메모 식별 + UI 표시용
+    source_external_id: str | None = None  # email 의 Message-ID 또는 imap UID fallback
+    email_subject: str | None = None  # email_metadata.subject — 메모 카드 부제 / 툴팁
     created_at: datetime
     updated_at: datetime
 
@@ -212,6 +215,8 @@ def _to_memo_response(doc: Document) -> MemoResponse:
         source_channel=doc.source_channel,
         file_type=doc.file_type,
         file_path=doc.file_path,
+        source_external_id=doc.source_external_id,
+        email_subject=(doc.email_metadata or {}).get('subject') if doc.email_metadata else None,
         created_at=doc.created_at,
         updated_at=doc.updated_at,
     )
@@ -274,8 +279,12 @@ async def list_memos(
     voice 메모는 file_type='immutable' + category='audio' + source_channel='voice' 패턴.
     source_channel 만으로 분리 (file_type 필터는 immutable 다른 binary 까지 끌어옴 — 회피).
     """
+    # PR-4: inbox_ingest 가 만든 email memo 도 포함 (source_external_id != NULL 로 mailplus_archive 의 archive row 제외)
     base = select(Document).where(
-        Document.source_channel.in_(("memo", "voice")),
+        or_(
+            Document.source_channel.in_(("memo", "voice")),
+            and_(Document.source_channel == "email", Document.source_external_id.isnot(None)),
+        ),
         Document.deleted_at == None,  # noqa: E711
         Document.archived == archived,
     )