Make ESC out of filter mode strictly synchronous

[Antoinegtir]

Scope

When the user presses / and then Esc, the filter is cleared but the cursor briefly stays in filter mode before the next render. On fast key-repeat it occasionally results in a single character bleeding through to action bindings.

What to do

• Trace through crates/fl-tui/src/runner.rs — the on_key ↔ filter_input ↔ keys_tx interaction.
• Make ESC handling synchronous: clear filter_input AND swallow the same tick so no action fires.

Acceptance

• Holding / + a letter + Esc never fires the bound action for that letter.
• Unit test on the key dispatch helper covers the transition.

Hint

The two existing call sites that check state.filter_input.is_some() before/after on_key are the right place to look.