Add fuzzy name search (pg_trgm) and living-person protection

Fuzzy search: pg_trgm extension + trigram GIN indexes on name parts and a GET /trees/{id}/persons?q= search ranked by trigram similarity (finds Mueller for 'muller'), privacy-filtered. Living-person protection: the privacy engine now derives possibly-living status (explicit flag, else no death fact + birth within ~100y or unknown) and returns 'redacted' for non-members of public/unlisted trees; the service minimises those records ('Living person', no vitals). Members are unaffected. 31 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/migrations/versions/9a2b1c7d4e10_pg_trgm_name_search.py

@@ -0,0 +1,33 @@
+"""pg_trgm extension + trigram name indexes for fuzzy search
+
+Revision ID: 9a2b1c7d4e10
+Revises: 7fc7024ef432
+Create Date: 2026-06-07
+
+"""
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "9a2b1c7d4e10"
+down_revision: str | None = "7fc7024ef432"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute("CREATE EXTENSION IF NOT EXISTS pg_trgm")
+    op.execute(
+        "CREATE INDEX IF NOT EXISTS ix_names_given_trgm "
+        "ON names USING gin (given gin_trgm_ops)"
+    )
+    op.execute(
+        "CREATE INDEX IF NOT EXISTS ix_names_surname_trgm "
+        "ON names USING gin (surname gin_trgm_ops)"
+    )
+
+
+def downgrade() -> None:
+    op.execute("DROP INDEX IF EXISTS ix_names_surname_trgm")
+    op.execute("DROP INDEX IF EXISTS ix_names_given_trgm")
+    # Leave the pg_trgm extension in place; other features may rely on it.