fix: reduce CPU spikes and freeze risk after query execution

[killertux]

Summary

Investigated reports of the TUI freezing with 100% CPU right after a query completes. lldb backtrace pinpointed the hang at kasuari::row::Row::insert_symbol — a known issue in the Cassowary solver ratatui 0.30 uses for Layout::split. See ratatui/kasuari#18: the simplex pivots cycle on degenerate ties when fed many identical Constraint::Min(_) constraints. Our result-table column widths were exactly that input.

Fixes

• Bypass kasuari for result columns (src/ui/results_view.rs) — primary fix. Replace [Constraint::Min(8); n] with hand-computed Constraint::Length(w) widths that even-split the inner width. distribute_columns now does the same arithmetic directly instead of calling Layout::horizontal(...).split(...). Same output shape; existing layout tests still pass. The kasuari solver no longer runs on the per-frame result render.
• Coalesce DDL-triggered schema reloads (src/app.rs, src/action/mod.rs) — added App::schema_reload_in_flight. Back-to-back DDLs no longer queue duplicate full-schema reintrospections; the flag clears on CacheStage::Reloaded and on Connected.
• Per-frame cell rendering (src/datasource/cell.rs + callers) — Cell::display() now returns Cow<'_, str>. Text / Decimal / Other { repr } borrow their existing String instead of cloning per visible cell per frame. ratatui clips to column width at draw time, so we no longer allocate megabytes per redraw for wide JSON/TEXT values.
• Autocomplete CTE parser (src/autocomplete/context.rs) — extract_projection_columns could re-enter its outer loop without i advancing if the inner scan hit an unbalanced inner ) at depth 0. Added a liveness guard so the worst case is a dropped projection, never a hang.

Bumps the patch version to 0.16.2.

Test plan

• cargo check clean
• cargo test --bin rowdy — 575 passed
• Run a query that previously froze the UI and confirm it no longer hangs
• Resize the terminal while a wide result is on screen (the kasuari issue thread flags resize as a common trigger)
• Sanity-check mouse hit-testing on result columns — the X-position arithmetic changed
• Sanity-check autocomplete inside a WITH cte AS (SELECT ... FROM t) body