v0.3.0 - Postgres full-text search

Added

• Postgres full-text search on Location: New search_vector
SearchVectorField on AbstractBaseLocation with a GIN index. The
  vector combines name (weight A) with string and numeric values from
  attributes JSONField (weight B), so attribute contents are
  searchable out of the box without per-project configuration.
• Auto-installed trigger: location_api_core wires a
  post_migrate signal that installs (and refreshes on every migrate) a
  Postgres trigger on each concrete AbstractBaseLocation subclass's
  table. Existing rows are backfilled on first run. Consumers only need to
  makemigrations after upgrading to pick up the new column and index.

Changed

• LocationSearchView now uses SearchQuery / SearchRank against
  the new search_vector (web-search syntax, simple FTS config),
  ordered by rank. Supplier name remains searchable via an OR'd
  icontains fallback, since supplier rename propagation is
  deliberately not part of the vector.