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

alembic/versions/0021_saved_filters.py

@@ -0,0 +1,35 @@
+"""saved_filters (richer search + saved views — M6 1902)
+
+Revision ID: 0021
+Revises: 0020
+Create Date: 2026-07-23
+
+A named facet combination the user can re-apply in one click. `params` is a
+JSON-encoded facet dict matching the GET /api/notes query.
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID
+
+revision = "0021"
+down_revision = "0020"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "saved_filters",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True),
+        sa.Column("owner_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("name", sa.Text(), nullable=False),
+        sa.Column("params", sa.Text(), nullable=False, server_default="{}"),
+        sa.Column("position", sa.Integer(), nullable=False, server_default="0"),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+    )
+    op.create_index("ix_saved_filters_owner", "saved_filters", ["owner_id", "position"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_saved_filters_owner", table_name="saved_filters")
+    op.drop_table("saved_filters")