v0.9.0 — PostgreSQL feature-freeze

PostgreSQL feature-freeze milestone: the explicit PostgreSQL backlog is now
complete. Next stop is 1.0 with multi-database (MySQL) support.

Added

• Table-level CSV/JSON export: a per-table "export" control on the table detail
  panel streams every row (read-only SELECT *, full table — not the preview's
  row cap) as a download, reusing the query exporter's streaming path.
• Filter builder on the table Data tab: stack column / operator (=, ≠, <, ≤, >,
  ≥, contains, starts with, is null, is not null) / value rows, ANDed, run as a
  read-only SELECT * … WHERE … (columns validated, values bound — never
  interpolated) and rendered in place.
• CSV import: append rows from an uploaded CSV into an existing table via COPY,
  matched by header name, in one all-or-nothing transaction (a bad row rolls the
  whole import back), with an automatic safety snapshot taken first.
• CLI2UI_DB_PATH environment variable to relocate the management SQLite file
  (e.g. onto a named Docker volume) — see README.NETWORKING.md.