namir-ui: Impulse Response and Output headings each render twice

[ErwanLegrand]

crates/namir-ui/src/app.rs:89/96 and :100/102

ui.heading("Impulse Response") is immediately followed by param_section(ui, "Impulse Response", "ir.", ...), which emits the same heading again (app.rs:139); same duplication for "Output". The shipped screen shows each of those two headings twice, separated only by the IR-name label or the output meter. The smoke test only asserts that rendering does not panic, so nothing catches it.

Fix: pass an empty title for those two sections, or drop the outer heading.

[ErwanLegrand]

Fixed in #145 (63afed5). param_section was split so a caller that puts something between a heading and its controls draws the heading itself and calls param_controls instead (crates/namir-ui/src/app.rs:225-247). render now paints "Impulse Response" once (app.rs:97, followed by the IR-name label and param_controls), and the "Output" heading is gone entirely — the meter row is already labelled "Output" and both controls under it are named "Output ...", so a heading would have been the third consecutive painting of the word (app.rs:110-112).

Guarded by each_section_heading_is_painted_exactly_once (app.rs:1018), driven at 1200x2400 so egui culls nothing below the fold. It also caught something this report's diagnosis did not name: "Output" had a third painting, the meter's own label, so removing the section title alone would have left two.

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