Atomic tview -> Bubble Tea v2 cutover (async execution, cancel, status, keymap)

One focused push, nothing else in flight (the port surface only grows while we wait). Built once, natively: DB calls as tea.Cmd (UI never blocks), Esc cancels in-flight query via ctx, single status/footer model (kills the time.AfterFunc races), keymap designed once — vim-style per-pane keys, no Ctrl-S/Q/D terminal collisions, configurable via config file. Includes the db->schema->table navigation model for Postgres deferred from v1.0.

**Acceptance:** teatest + golden-frame suite green; feature parity with the tview UI per the characterization suite; UI responsive during a deliberately slow query, Esc aborts it.

Start with the teatest, golden-frame, and characterization suites to establish the existing tview behavior and feature parity. Exercise the UI with a deliberately slow query, then verify that the suites are green, the UI remains responsive, and Esc aborts the in-flight query.

Written by the indexing model from the issue text.