fix(ui): make UI scale work in DAWs (live zoom + window resize)

[Hornfisk]

Fixes #3.

Problem

The UI 1.5x badge only wrote ui_scale.txt (read solely by the standalone launcher via --dpi-scale). In a DAW nothing read it and Editor::set_scale_factor was never driven from it, so clicking the badge — and resizing the window — did nothing in every host.

Fix

Drive egui content zoom + a matching programmatic window resize from one scale value, every frame:

ctx.set_zoom_factor(scale);
if editor_state.size() != BASE_WINDOW_SIZE * scale {
    editor_state.set_requested_size(...);
}

With baseview's native scale pinned to 1.0 (DAW hosts default to it; the launcher now passes --dpi-scale 1.0), effective ppp == scale: the host window grows to 680×444 × scale physical px while the layout keeps drawing into a fixed 680×444 logical space. Uniform scale, no reflow — knob rows never move relative to each other.

Changes

• src/ui/editor.rs — per-frame zoom + resize reconcile; honest badge tooltip/log.
• src/params.rs — open pre-scaled (new BASE_WINDOW_SIZE const) to avoid a first-frame resize flash.
• tools/niner-launch.sh — pin --dpi-scale 1.0; plugin owns scaling now.
• Cargo.toml — repoint nih_plug/nih_plug_egui to Hornfisk/nih-plug@8b51e93 (upstream 28b149e + one line exposing EguiState::set_requested_size, private upstream — mirrors the existing Hornfisk/baseview patch pattern).

Verification

• ✅ cargo check clean; cargo test green (7 tests).
• ⚠️ Needs DAW verification on geek (couldn't test from WSL): open in Reaper, click badge through 1x/1.5x/2x → window + content scale live, layout intact, knobs aligned. Repeat in Bitwig (texture-cache reopen path) and standalone via niner-launch.sh. If a host ignores request_resize, it degrades to opening at the right size (still better than today).

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