Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/api/search.py

@@ -0,0 +1,64 @@
+"""Search endpoint (SPEC §9.1 Search, §8). Results grouped by thread (FR-28)."""
+
+from __future__ import annotations
+
+import uuid
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, Query
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.api.schemas import SearchOut, SearchThreadHit
+from app.api.threads import _summary
+from app.db import get_session
+from app.identity.deps import CurrentUser
+from app.models import Thread
+from app.search.factory import get_search_backend
+from app.search.queryparser import to_search_query
+
+router = APIRouter(prefix="/search", tags=["search"])
+
+DbSession = Annotated[AsyncSession, Depends(get_session)]
+
+
+@router.get("", response_model=SearchOut)
+async def search(
+    user: CurrentUser,
+    db: DbSession,
+    q: str = Query(""),
+    cursor: str | None = None,
+    limit: int = Query(50, ge=1, le=200),
+) -> SearchOut:
+    if not q.strip():
+        return SearchOut(threads=[], cursor=None)
+
+    backend = get_search_backend()
+    query = to_search_query(q, user.id)
+    hits, next_cursor = await backend.query(query, limit=limit, cursor=cursor)
+
+    # Group hits by thread, preserving order and keeping the first highlight.
+    order: list[uuid.UUID] = []
+    highlights: dict[uuid.UUID, dict[str, str]] = {}
+    for hit in hits:
+        if hit.thread_id not in highlights:
+            order.append(hit.thread_id)
+            highlights[hit.thread_id] = hit.highlights
+        elif hit.highlights and not highlights[hit.thread_id]:
+            highlights[hit.thread_id] = hit.highlights
+
+    if not order:
+        return SearchOut(threads=[], cursor=next_cursor)
+
+    threads = {
+        t.id: t
+        for t in await db.scalars(
+            select(Thread).where(Thread.id.in_(order), Thread.user_id == user.id)
+        )
+    }
+    results = [
+        SearchThreadHit(thread=_summary(threads[tid]), highlights=highlights.get(tid, {}))
+        for tid in order
+        if tid in threads
+    ]
+    return SearchOut(threads=results, cursor=next_cursor)