M6 1902a: richer facet query + saved-filters storage (backend)

GET /api/notes gains combinable, AND-ed facets alongside the existing
filter/date/sort: multiple ?label= (notes with ALL), ?color, ?kind,
?has_reminder, ?has_attachment, and ?q (full-text over title+body, ranked)
— so the facet bar's text box searches, not just filters. All optional;
invalid color/kind → 400.

saved_filters table (migration 0021) + /api/saved-filters CRUD (list /
create / rename+repoint / delete, owner-scoped). `params` is a JSON facet
dict mirroring the query surface; clean_params() whitelists facet keys so a
saved view can't accumulate junk.

Tests (DB-free): _truthy, clean_params key-whitelisting, saved-filters
auth-guards. UI (facet bar + saved-views sidebar) lands next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

src/thoughtsync/models/all.py

@@ -13,6 +13,7 @@ from . import (  # noqa: F401
     note_link,
     note_link_preview,
     note_revision,
+    saved_filter,
     settings,
     share,
     user,

src/thoughtsync/models/saved_filter.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Integer, Text, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from . import Base
+
+
+class SavedFilter(Base):
+    """A named, saved facet combination (a 'view'/lens) the user can re-apply in one
+    click — e.g. "Yellow + #ideas". `params` is a JSON-encoded facet dict matching the
+    GET /api/notes query (q/color/kind/labels/has_reminder/has_attachment/date range)."""
+
+    __tablename__ = "saved_filters"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    owner_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    name: Mapped[str] = mapped_column(Text(), nullable=False)
+    params: Mapped[str] = mapped_column(Text(), nullable=False, server_default="{}")
+    position: Mapped[int] = mapped_column(Integer(), nullable=False, server_default="0")
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now())